[PATCH v2 00/53] objtool/klp: Some klp-build fixes and improvements

[PATCH v2 00/53] objtool/klp: Some klp-build fixes and improvements

[Josh Poimboeuf]

Changes since v1 (https://lore.kernel.org/cover.1776916871.git.jpoimboe@kernel.org):

- Add comment for find_reloc_by_dest_range() first-match behavior
  [Peter]
- Simplify is_cold_func() [Peter]
- Grow __cfi_ symbols [Peter]
- Rename "Ignore __UNIQUE_ID_*() PCI stub functions" to more general
  "Don't report uncorrelated functions as new" [Song]
- Move rodata non-correlation into pointer-comparison fix [Miroslav]
- Add comments for convert_reloc_sym() return values [Song]
- Remove redundant SRC/OBJ variables [Song]
- Use "if (mismatch) {} else" in for_each_sym_by_*() [Song]
- Flatten nested if-else chain in short-circuit validation [Song]
- Add comments with examples to symbol correlation algorithm [Song]
- Move callback refactor to earlier in the patch set [Miroslav]
- Fix reloc corruption in convert_reloc_sym_to_secsym() [Sashiko]
- Include offset in object checksum hashing [Sashiko]
- Fix klp-build checksum comparison output for added/removed
  instructions [Sashiko]
- Fix kCFI prefix finding/cloning
- Add reloc symbol conversion simplification cleanup
- Improve local label check for uncorrelated symbols
- Drop "Make function prefix handling more generic" for now (refactored
  version will come with arm64 patches)
- Refactor inline alternative cloning into separate
  clone_inline_alternatives()
- Add Acked-by/Reviewed-by tags

---

While working on the (upcoming) arm64 support, I ended up shaking out a
lot of bugs by tested several patches on a variety of configs (distro,
LTO, FineIBT, kCFI, etc).

While arm64 support seems to be working well, I decided to leave those
patches out of this set to try to keep the number of patches
"reasonable".

And these stand alone as nice improvements for x86 anyway.

Full arm64 support (this set + more) can be found here:

  git://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git klp-build-arm64

Joe Lawrence (2):
  objtool/klp: Fix is_uncorrelated_static_local() for Clang
  objtool/klp: Fix create_fake_symbols() skipping entsize-based sections

Josh Poimboeuf (51):
  objtool/klp: Fix .data..once static local non-correlation
  objtool/klp: Don't correlate __ADDRESSABLE() symbols
  objtool/klp: Don't correlate absolute symbols
  objtool/klp: Don't correlate __initstub__ symbols
  objtool/klp: Don't report uncorrelated functions as new
  objtool/klp: Improve local label check
  objtool: Replace iterator callback with for_each_sym_by_mangled_name()
  objtool/klp: Fix --debug-checksum for duplicate symbol names
  objtool/klp: Fix handling of zero-length .altinstr_replacement
    sections
  objtool/klp: Fix cloning of zero-length section symbols
  objtool/klp: Fix XXH3 state memory leak
  objtool/klp: Fix extraction of text annotations for alternatives
  objtool/klp: Fix kCFI trap handling
  objtool/klp: Fix relocation conversion failures for R_X86_64_NONE
  objtool: Move mark_rodata() to elf.c
  objtool/klp: Simplify reloc symbol conversion
  objtool/klp: Fix pointer comparisons for rodata objects
  objtool/klp: Don't correlate .rodata.cst* constant pool objects
  objtool/klp: Fix reloc corruption in convert_reloc_sym_to_secsym()
  objtool: Fix reloc hash collision in find_reloc_by_dest_range()
  klp-build: Fix hang on out-of-date .config
  klp-build: Fix checksum comparison for changed offsets
  klp-build: Don't use errexit
  klp-build: Validate patch file existence
  klp-build: Suppress excessive fuzz output by default
  klp-build: Fix patch cleanup on interrupt
  klp-build: Reject patches to vDSO
  klp-build: Reject patches to realmode
  klp-build: Print "objtool klp diff" command in verbose mode
  klp-build: Remove redundant SRC and OBJ variables
  objtool/klp: Don't set sym->file for section symbols
  objtool: Include libsubcmd headers directly from source tree
  objtool/klp: Create empty checksum sections for function-less object
    files
  objtool/klp: Handle Clang .data..Lanon anonymous data sections
  objtool: Add is_alias_sym() helper
  objtool: Add is_cold_func() helper
  objtool/klp: Extricate checksum calculation from validate_branch()
  objtool: Consolidate file decoding into decode_file()
  objtool/klp: Add "objtool klp checksum" subcommand
  klp-build: Use "objtool klp checksum" subcommand
  objtool/klp: Remove "objtool --checksum"
  klp-build: Validate short-circuit prerequisites
  objtool/klp: Calculate object checksums
  objtool/klp: Rewrite symbol correlation algorithm
  objtool/klp: Add correlation debugging output
  objtool: Add insn_sym() helper
  objtool/klp: Fix position-dependent checksums for non-relocated
    jumps/calls
  objtool: Grow __cfi_* prefix symbols for all CFI+CALL_PADDING
  objtool/klp: Fix kCFI prefix finding/cloning
  objtool: Improve and simplify prefix symbol detection
  objtool/klp: Cache dont_correlate() result

 arch/x86/Kconfig                         |   4 -
 lib/Kconfig.debug                        |   2 +-
 scripts/Makefile.lib                     |   7 +-
 scripts/livepatch/klp-build              | 250 ++++---
 tools/objtool/Build                      |   2 +-
 tools/objtool/Makefile                   |   4 +-
 tools/objtool/arch/x86/decode.c          |  17 +-
 tools/objtool/builtin-check.c            |  26 +-
 tools/objtool/builtin-klp.c              |   1 +
 tools/objtool/check.c                    | 412 ++++-------
 tools/objtool/disas.c                    |  22 +-
 tools/objtool/elf.c                      | 124 ++--
 tools/objtool/include/objtool/arch.h     |   3 +
 tools/objtool/include/objtool/builtin.h  |   7 +-
 tools/objtool/include/objtool/check.h    |  34 +-
 tools/objtool/include/objtool/checksum.h |  53 +-
 tools/objtool/include/objtool/elf.h      |  59 +-
 tools/objtool/include/objtool/klp.h      |   1 +
 tools/objtool/include/objtool/warn.h     |  57 +-
 tools/objtool/klp-checksum.c             | 347 ++++++++++
 tools/objtool/klp-diff.c                 | 826 ++++++++++++++++-------
 tools/objtool/objtool.c                  |   3 -
 tools/objtool/trace.c                    |   8 +-
 23 files changed, 1493 insertions(+), 776 deletions(-)
 create mode 100644 tools/objtool/klp-checksum.c

-- 
2.53.0

[PATCH v2 01/53] objtool/klp: Fix is_uncorrelated_static_local() for Clang

[Josh Poimboeuf]

From: Joe Lawrence <joe.lawrence@redhat.com>

For naming function-local static locals, GCC uses <var>.<id>, e.g.
__already_done.15, while Clang uses <func>.<var> with optional .<id>,
e.g. create_worker.__already_done.111

The existing is_uncorrelated_static_local() check only matches the GCC
convention where the variable name is a prefix.  Handle both cases by
checking for a prefix match (GCC) and by checking after the first dot
separator (Clang).

Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 0b0d1503851f..b1b068e9b4c7 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -242,16 +242,17 @@ static struct symbol *next_file_symbol(struct elf *elf, struct symbol *sym)
 static bool is_uncorrelated_static_local(struct symbol *sym)
 {
 	static const char * const vars[] = {
-		"__already_done.",
-		"__func__.",
-		"__key.",
-		"__warned.",
-		"_entry.",
-		"_entry_ptr.",
-		"_rs.",
-		"descriptor.",
-		"CSWTCH.",
+		"__already_done",
+		"__func__",
+		"__key",
+		"__warned",
+		"_entry",
+		"_entry_ptr",
+		"_rs",
+		"descriptor",
+		"CSWTCH",
 	};
+	const char *dot;
 
 	if (!is_object_sym(sym) || !is_local_sym(sym))
 		return false;
@@ -259,8 +260,20 @@ static bool is_uncorrelated_static_local(struct symbol *sym)
 	if (!strcmp(sym->sec->name, ".data.once"))
 		return true;
 
+	dot = strchr(sym->name, '.');
+	if (!dot)
+		return false;
+
 	for (int i = 0; i < ARRAY_SIZE(vars); i++) {
-		if (strstarts(sym->name, vars[i]))
+		size_t len = strlen(vars[i]);
+
+		/* GCC: <var>.<id> */
+		if (strstarts(sym->name, vars[i]) && (sym->name[len] == '.'))
+			return true;
+
+		/* Clang: <func>.<var>[.<id>] */
+		if (strstarts(dot + 1, vars[i]) &&
+		    (dot[1 + len] == '.' || dot[1 + len] == '\0'))
 			return true;
 	}
 
-- 
2.53.0

[PATCH v2 02/53] objtool/klp: Fix .data..once static local non-correlation

[Josh Poimboeuf]

While there was once a section named .data.once, it has since been
renamed to .data..once with commit dbefa1f31a91 ("Rename .data.once to
.data..once to fix resetting WARN*_ONCE").  Fix it.

Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index b1b068e9b4c7..cb26c1c92a74 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -257,7 +257,8 @@ static bool is_uncorrelated_static_local(struct symbol *sym)
 	if (!is_object_sym(sym) || !is_local_sym(sym))
 		return false;
 
-	if (!strcmp(sym->sec->name, ".data.once"))
+	/* WARN_ONCE, etc */
+	if (!strcmp(sym->sec->name, ".data..once"))
 		return true;
 
 	dot = strchr(sym->name, '.');
-- 
2.53.0

[PATCH v2 03/53] objtool/klp: Don't correlate __ADDRESSABLE() symbols

[Josh Poimboeuf]

Symbols created by __ADDRESSABLE() are only used to convince the
toolchain not to optimize out the referenced symbol.

Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index cb26c1c92a74..36753eeba58c 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -352,6 +352,15 @@ static bool is_special_section_aux(struct section *sec)
 	return false;
 }
 
+/*
+ * Symbols created by ___ADDRESSABLE() are only used to convince the toolchain
+ * not to optimize out the referenced symbol.
+ */
+static bool is_addressable_sym(struct symbol *sym)
+{
+	return !strcmp(sym->sec->name, ".discard.addressable");
+}
+
 /*
  * These symbols should never be correlated, so their local patched versions
  * are used instead of linking to the originals.
@@ -365,6 +374,7 @@ static bool dont_correlate(struct symbol *sym)
 	       is_uncorrelated_static_local(sym) ||
 	       is_clang_tmp_label(sym) ||
 	       is_string_sec(sym->sec) ||
+	       is_addressable_sym(sym) ||
 	       is_special_section(sym->sec) ||
 	       is_special_section_aux(sym->sec) ||
 	       strstarts(sym->name, "__initcall__");
-- 
2.53.0

Re: [PATCH v2 03/53] objtool/klp: Don't correlate __ADDRESSABLE() symbols

[Song Liu]

On Fri, May 1, 2026 at 5:08 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> Symbols created by __ADDRESSABLE() are only used to convince the
> toolchain not to optimize out the referenced symbol.
>
> Reviewed-by: Miroslav Benes <mbenes@suse.cz>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

[PATCH v2 04/53] objtool/klp: Don't correlate absolute symbols

[Josh Poimboeuf]

Some arch/x86/crypto/*.S files define local .set/.equ constants that get
duplicated in vmlinux.o.  This causes klp-diff to fail with "Multiple
correlation candidates" errors since it can't uniquely match these
between orig and patched builds.

Skip ABS symbols in dont_correlate().  They're purely compile-time
assembly constants that are never referenced by relocations, so they
don't need correlation.

Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 36753eeba58c..27ebe1b1f463 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -361,6 +361,15 @@ static bool is_addressable_sym(struct symbol *sym)
 	return !strcmp(sym->sec->name, ".discard.addressable");
 }
 
+/*
+ * ABS symbols are typically assembly .set/.equ constants which are never
+ * referenced by relocations.  (Exclude FILE symbols which are also SHN_ABS.)
+ */
+static bool is_abs_sym(struct symbol *sym)
+{
+	return sym->sym.st_shndx == SHN_ABS && !is_file_sym(sym);
+}
+
 /*
  * These symbols should never be correlated, so their local patched versions
  * are used instead of linking to the originals.
@@ -370,6 +379,7 @@ static bool dont_correlate(struct symbol *sym)
 	return is_file_sym(sym) ||
 	       is_null_sym(sym) ||
 	       is_sec_sym(sym) ||
+	       is_abs_sym(sym) ||
 	       is_prefix_func(sym) ||
 	       is_uncorrelated_static_local(sym) ||
 	       is_clang_tmp_label(sym) ||
-- 
2.53.0

[PATCH v2 05/53] objtool/klp: Don't correlate __initstub__ symbols

[Josh Poimboeuf]

With LTO, the initcall infrastructure generates __initstub__kmod_*
wrapper functions in .init.text.  These are the LTO equivalent of
__initcall__kmod_* data pointers, which are already excluded from
correlation.

These are __init functions whose memory is freed after boot, so there's
no reason to include or reference them in a livepatch module.

Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 27ebe1b1f463..4f668117c45e 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -370,6 +370,12 @@ static bool is_abs_sym(struct symbol *sym)
 	return sym->sym.st_shndx == SHN_ABS && !is_file_sym(sym);
 }
 
+static bool is_initcall_sym(struct symbol *sym)
+{
+	return strstarts(sym->name, "__initcall__") ||
+	       strstarts(sym->name, "__initstub__");
+}
+
 /*
  * These symbols should never be correlated, so their local patched versions
  * are used instead of linking to the originals.
@@ -384,10 +390,10 @@ static bool dont_correlate(struct symbol *sym)
 	       is_uncorrelated_static_local(sym) ||
 	       is_clang_tmp_label(sym) ||
 	       is_string_sec(sym->sec) ||
+	       is_initcall_sym(sym) ||
 	       is_addressable_sym(sym) ||
 	       is_special_section(sym->sec) ||
-	       is_special_section_aux(sym->sec) ||
-	       strstarts(sym->name, "__initcall__");
+	       is_special_section_aux(sym->sec);
 }
 
 struct process_demangled_name_data {
-- 
2.53.0

[PATCH v2 06/53] objtool/klp: Don't report uncorrelated functions as new

[Josh Poimboeuf]

Clang LTO uses __UNIQUE_ID() to generate some uniquely named wrapper
functions, like initstubs.  If they're uncorrelated, prevent them from
being reported as new functions and included unnecessarily.

Note that dont_correlate() already includes prefix functions, so prefix
functions are still being ignored here.

Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 4f668117c45e..ccb16a45107e 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -802,7 +802,7 @@ static int mark_changed_functions(struct elfs *e)
 
 	/* Find changed functions */
 	for_each_sym(e->orig, sym_orig) {
-		if (!is_func_sym(sym_orig) || is_prefix_func(sym_orig))
+		if (!is_func_sym(sym_orig) || dont_correlate(sym_orig))
 			continue;
 
 		patched_sym = sym_orig->twin;
@@ -818,7 +818,7 @@ static int mark_changed_functions(struct elfs *e)
 
 	/* Find added functions and print them */
 	for_each_sym(e->patched, patched_sym) {
-		if (!is_func_sym(patched_sym) || is_prefix_func(patched_sym))
+		if (!is_func_sym(patched_sym) || dont_correlate(patched_sym))
 			continue;
 
 		if (!patched_sym->twin) {
-- 
2.53.0

[PATCH v2 07/53] objtool/klp: Improve local label check

[Josh Poimboeuf]

Clang emits various .L-prefixed local symbols beyond .Ltmp*, such as
.L__const.* for local constant data.  These are assembler-local labels
not present in kallsyms, so they can never be resolved at module load
time.

Broaden the check from .Ltmp* to all .L* symbols so they get cloned into
the patch module instead.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index ccb16a45107e..c5d4c9ed8580 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -282,14 +282,14 @@ static bool is_uncorrelated_static_local(struct symbol *sym)
 }
 
 /*
- * Clang emits several useless .Ltmp_* code labels.
+ * .L symbols are assembler-local labels not present in kallsyms.  They must
+ * never become KLP relocations; instead their data is cloned into the patch
+ * module.  This covers .Ltmp* (Clang temp labels), .L__const.* (Clang local
+ * constants), and any other assembler-local pattern.
  */
-static bool is_clang_tmp_label(struct symbol *sym)
+static bool is_local_label(struct symbol *sym)
 {
-	return is_notype_sym(sym) &&
-	       is_text_sec(sym->sec) &&
-	       strstarts(sym->name, ".Ltmp") &&
-	       isdigit(sym->name[5]);
+	return strstarts(sym->name, ".L");
 }
 
 static bool is_special_section(struct section *sec)
@@ -388,7 +388,7 @@ static bool dont_correlate(struct symbol *sym)
 	       is_abs_sym(sym) ||
 	       is_prefix_func(sym) ||
 	       is_uncorrelated_static_local(sym) ||
-	       is_clang_tmp_label(sym) ||
+	       is_local_label(sym) ||
 	       is_string_sec(sym->sec) ||
 	       is_initcall_sym(sym) ||
 	       is_addressable_sym(sym) ||
-- 
2.53.0

Re: [PATCH v2 07/53] objtool/klp: Improve local label check

[Song Liu]

On Fri, May 1, 2026 at 5:08 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> Clang emits various .L-prefixed local symbols beyond .Ltmp*, such as
> .L__const.* for local constant data.  These are assembler-local labels
> not present in kallsyms, so they can never be resolved at module load
> time.
>
> Broaden the check from .Ltmp* to all .L* symbols so they get cloned into
> the patch module instead.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

[PATCH v2 08/53] objtool/klp: Fix create_fake_symbols() skipping entsize-based sections

[Josh Poimboeuf]

From: Joe Lawrence <joe.lawrence@redhat.com>

create_fake_symbols() has two phases: creating symbols from
ANNOTATE_DATA_SPECIAL entries, and a fallback that uses sh_entsize for
special sections like .static_call_sites.

When .discard.annotate_data is absent, the function returns early,
skipping the entsize fallback and silently allowing unsupported
module-local static call keys through.

Fix it by jumping to the entsize phase instead of returning early.

Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Assisted-by: Claude:claude-4-opus
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index c5d4c9ed8580..0653bf6a33bd 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -1374,7 +1374,7 @@ static int create_fake_symbols(struct elf *elf)
 
 	sec = find_section_by_name(elf, ".discard.annotate_data");
 	if (!sec || !sec->rsec)
-		return 0;
+		goto entsize;
 
 	for_each_reloc(sec->rsec, reloc) {
 		unsigned long offset, size;
@@ -1406,7 +1406,7 @@ static int create_fake_symbols(struct elf *elf)
 	/*
 	 * 2) Make symbols for sh_entsize, and simple arrays of pointers:
 	 */
-
+entsize:
 	for_each_sec(elf, sec) {
 		unsigned int entry_size;
 		unsigned long offset;
-- 
2.53.0

[PATCH v2 09/53] objtool: Replace iterator callback with for_each_sym_by_mangled_name()

[Josh Poimboeuf]

Convert the callback-based iterate_sym_by_demangled_name() with a new
for_each_sym_by_demangled_name() macro.  This eliminates the callback
struct/function and makes the code more compact and readable.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/elf.c                 | 68 ++++++++---------------------
 tools/objtool/include/objtool/elf.h | 32 ++++++++++++--
 tools/objtool/klp-diff.c            | 42 ++++++------------
 3 files changed, 60 insertions(+), 82 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index f3df2bde119f..dc39132f71c1 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -27,27 +27,16 @@
 
 static ssize_t demangled_name_len(const char *name);
 
-static inline u32 str_hash(const char *str)
-{
-	return jhash(str, strlen(str), 0);
-}
-
-static inline u32 str_hash_demangled(const char *str)
+u32 str_hash_demangled(const char *str)
 {
 	return jhash(str, demangled_name_len(str), 0);
 }
 
-#define __elf_table(name)	(elf->name##_hash)
-#define __elf_bits(name)	(elf->name##_bits)
-
-#define __elf_table_entry(name, key) \
-	__elf_table(name)[hash_min(key, __elf_bits(name))]
-
 #define elf_hash_add(name, node, key)					\
 ({									\
 	struct elf_hash_node *__node = node;				\
-	__node->next = __elf_table_entry(name, key);			\
-	__elf_table_entry(name, key) = __node;				\
+	__node->next = __elf_table_entry(elf, name, key);		\
+	__elf_table_entry(elf, name, key) = __node;			\
 })
 
 static inline void __elf_hash_del(struct elf_hash_node *node,
@@ -69,30 +58,20 @@ static inline void __elf_hash_del(struct elf_hash_node *node,
 }
 
 #define elf_hash_del(name, node, key) \
-	__elf_hash_del(node, &__elf_table_entry(name, key))
-
-#define elf_list_entry(ptr, type, member)				\
-({									\
-	typeof(ptr) __ptr = (ptr);					\
-	__ptr ? container_of(__ptr, type, member) : NULL;		\
-})
-
-#define elf_hash_for_each_possible(name, obj, member, key)		\
-	for (obj = elf_list_entry(__elf_table_entry(name, key), typeof(*obj), member); \
-	     obj;							\
-	     obj = elf_list_entry(obj->member.next, typeof(*(obj)), member))
+	__elf_hash_del(node, &__elf_table_entry(elf, name, key))
 
 #define elf_alloc_hash(name, size)					\
 ({									\
-	__elf_bits(name) = max(10, ilog2(size));			\
-	__elf_table(name) = mmap(NULL, sizeof(struct elf_hash_node *) << __elf_bits(name), \
+	__elf_bits(elf, name) = max(10, ilog2(size));			\
+	__elf_table(elf, name) = mmap(NULL,				\
+				 sizeof(struct elf_hash_node *) << __elf_bits(elf, name), \
 				 PROT_READ|PROT_WRITE,			\
 				 MAP_PRIVATE|MAP_ANON, -1, 0);		\
-	if (__elf_table(name) == (void *)-1L) {				\
+	if (__elf_table(elf, name) == (void *)-1L) {			\
 		ERROR_GLIBC("mmap fail " #name);			\
-		__elf_table(name) = NULL;				\
+		__elf_table(elf, name) = NULL;				\
 	}								\
-	__elf_table(name);						\
+	__elf_table(elf, name);						\
 })
 
 static inline unsigned long __sym_start(struct symbol *s)
@@ -141,7 +120,7 @@ struct section *find_section_by_name(const struct elf *elf, const char *name)
 {
 	struct section *sec;
 
-	elf_hash_for_each_possible(section_name, sec, name_hash, str_hash(name)) {
+	elf_hash_for_each_possible(elf, section_name, sec, name_hash, str_hash(name)) {
 		if (!strcmp(sec->name, name))
 			return sec;
 	}
@@ -154,7 +133,7 @@ static struct section *find_section_by_index(struct elf *elf,
 {
 	struct section *sec;
 
-	elf_hash_for_each_possible(section, sec, hash, idx) {
+	elf_hash_for_each_possible(elf, section, sec, hash, idx) {
 		if (sec->idx == idx)
 			return sec;
 	}
@@ -166,7 +145,7 @@ static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
 {
 	struct symbol *sym;
 
-	elf_hash_for_each_possible(symbol, sym, hash, idx) {
+	elf_hash_for_each_possible(elf, symbol, sym, hash, idx) {
 		if (sym->idx == idx)
 			return sym;
 	}
@@ -285,7 +264,7 @@ struct symbol *find_symbol_by_name(const struct elf *elf, const char *name)
 {
 	struct symbol *sym;
 
-	elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash(name)) {
+	elf_hash_for_each_possible(elf, symbol_name, sym, name_hash, str_hash(name)) {
 		if (!strcmp(sym->name, name))
 			return sym;
 	}
@@ -300,7 +279,7 @@ static struct symbol *find_local_symbol_by_file_and_name(const struct elf *elf,
 {
 	struct symbol *sym;
 
-	elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash_demangled(name)) {
+	elf_hash_for_each_possible(elf, symbol_name, sym, name_hash, str_hash_demangled(name)) {
 		if (sym->bind == STB_LOCAL && sym->file == file &&
 		    !strcmp(sym->name, name)) {
 			return sym;
@@ -314,7 +293,7 @@ struct symbol *find_global_symbol_by_name(const struct elf *elf, const char *nam
 {
 	struct symbol *sym;
 
-	elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash_demangled(name)) {
+	elf_hash_for_each_possible(elf, symbol_name, sym, name_hash, str_hash_demangled(name)) {
 		if (!strcmp(sym->name, name) && !is_local_sym(sym))
 			return sym;
 	}
@@ -322,19 +301,6 @@ struct symbol *find_global_symbol_by_name(const struct elf *elf, const char *nam
 	return NULL;
 }
 
-void iterate_global_symbol_by_demangled_name(const struct elf *elf,
-					     const char *demangled_name,
-					     void (*process)(struct symbol *sym, void *data),
-					     void *data)
-{
-	struct symbol *sym;
-
-	elf_hash_for_each_possible(symbol_name, sym, name_hash, str_hash(demangled_name)) {
-		if (!strcmp(sym->demangled_name, demangled_name) && !is_local_sym(sym))
-			process(sym, data);
-	}
-}
-
 struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
 				     unsigned long offset, unsigned int len)
 {
@@ -347,7 +313,7 @@ struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *se
 		return NULL;
 
 	for_offset_range(o, offset, offset + len) {
-		elf_hash_for_each_possible(reloc, reloc, hash,
+		elf_hash_for_each_possible(elf, reloc, reloc, hash,
 					   sec_offset_hash(rsec, o)) {
 			if (reloc->sec != rsec)
 				continue;
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index 25573e5af76e..b142984eb9b5 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -21,6 +21,13 @@
 #define SEC_NAME_LEN		1024
 #define SYM_NAME_LEN		512
 
+static inline u32 str_hash(const char *str)
+{
+	return jhash(str, strlen(str), 0);
+}
+
+u32 str_hash_demangled(const char *str);
+
 #define bswap_if_needed(elf, val) __bswap_if_needed(&elf->ehdr, val)
 
 #ifdef LIBELF_USE_DEPRECATED
@@ -130,6 +137,23 @@ struct elf {
 	struct symbol *symbol_data;
 };
 
+#define __elf_table(elf, name)	((elf)->name##_hash)
+#define __elf_bits(elf, name)	((elf)->name##_bits)
+
+#define __elf_table_entry(elf, name, key) \
+	__elf_table(elf, name)[hash_min(key, __elf_bits(elf, name))]
+
+#define elf_list_entry(ptr, type, member)				\
+({									\
+	typeof(ptr) __ptr = (ptr);					\
+	__ptr ? container_of(__ptr, type, member) : NULL;		\
+})
+
+#define elf_hash_for_each_possible(elf, name, obj, member, key)		\
+	for (obj = elf_list_entry(__elf_table_entry(elf, name, key), typeof(*obj), member); \
+	     obj;							\
+	     obj = elf_list_entry(obj->member.next, typeof(*(obj)), member))
+
 struct elf *elf_open_read(const char *name, int flags);
 struct elf *elf_create_file(GElf_Ehdr *ehdr, const char *name);
 
@@ -186,9 +210,6 @@ struct symbol *find_func_by_offset(struct section *sec, unsigned long offset);
 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset);
 struct symbol *find_symbol_by_name(const struct elf *elf, const char *name);
 struct symbol *find_global_symbol_by_name(const struct elf *elf, const char *name);
-void iterate_global_symbol_by_demangled_name(const struct elf *elf, const char *demangled_name,
-					     void (*process)(struct symbol *sym, void *data),
-					     void *data);
 struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset);
 int find_symbol_hole_containing(const struct section *sec, unsigned long offset);
 struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset);
@@ -468,6 +489,11 @@ static inline void set_sym_next_reloc(struct reloc *reloc, struct reloc *next)
 #define for_each_sym_continue(elf, sym)					\
 	list_for_each_entry_continue(sym, &elf->symbols, global_list)
 
+#define for_each_sym_by_demangled_name(elf, name, sym)			\
+	elf_hash_for_each_possible(elf, symbol_name, sym, name_hash,	\
+				   str_hash(name))			\
+		if (strcmp(sym->demangled_name, name)) {} else
+
 #define rsec_next_reloc(rsec, reloc)					\
 	reloc_idx(reloc) < sec_num_entries(rsec) - 1 ? reloc + 1 : NULL
 
diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 0653bf6a33bd..30ce234e01a1 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -46,11 +46,6 @@ static const struct option klp_diff_options[] = {
 
 static DEFINE_HASHTABLE(exports, 15);
 
-static inline u32 str_hash(const char *str)
-{
-	return jhash(str, strlen(str), 0);
-}
-
 static char *escape_str(const char *orig)
 {
 	size_t len = 0;
@@ -396,22 +391,6 @@ static bool dont_correlate(struct symbol *sym)
 	       is_special_section_aux(sym->sec);
 }
 
-struct process_demangled_name_data {
-	struct symbol *ret;
-	int count;
-};
-
-static void process_demangled_name(struct symbol *sym, void *d)
-{
-	struct process_demangled_name_data *data = d;
-
-	if (sym->twin)
-		return;
-
-	data->count++;
-	data->ret = sym;
-}
-
 /*
  * When there is no full name match, try match demangled_name. This would
  * match original foo.llvm.123 to patched foo.llvm.456.
@@ -423,16 +402,23 @@ static void process_demangled_name(struct symbol *sym, void *d)
 static int find_global_symbol_by_demangled_name(struct elf *elf, struct symbol *sym,
 						struct symbol **out_sym)
 {
-	struct process_demangled_name_data data = {};
+	struct symbol *sym2, *result = NULL;
+	int count = 0;
 
-	iterate_global_symbol_by_demangled_name(elf, sym->demangled_name,
-						process_demangled_name,
-						&data);
-	if (data.count > 1) {
-		ERROR("Multiple (%d) correlation candidates for %s", data.count, sym->name);
+	for_each_sym_by_demangled_name(elf, sym->demangled_name, sym2) {
+		if (is_local_sym(sym2) || sym2->twin)
+			continue;
+
+		count++;
+		result = sym2;
+	}
+
+	if (count > 1) {
+		ERROR("Multiple (%d) correlation candidates for %s", count, sym->name);
 		return -1;
 	}
-	*out_sym = data.ret;
+
+	*out_sym = result;
 	return 0;
 }
 
-- 
2.53.0

Re: [PATCH v2 09/53] objtool: Replace iterator callback with for_each_sym_by_mangled_name()

[Song Liu]

On Fri, May 1, 2026 at 5:08 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> Convert the callback-based iterate_sym_by_demangled_name() with a new
> for_each_sym_by_demangled_name() macro.  This eliminates the callback
> struct/function and makes the code more compact and readable.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

Re: [PATCH v2 09/53] objtool: Replace iterator callback with for_each_sym_by_mangled_name()

[Miroslav Benes]

On Thu, 30 Apr 2026 21:07:57 -0700, Josh Poimboeuf <jpoimboe@kernel.org> wrote:
> Convert the callback-based iterate_sym_by_demangled_name() with a new
> for_each_sym_by_demangled_name() macro.  This eliminates the callback
> struct/function and makes the code more compact and readable.

Reviewed-by: Miroslav Benes <mbenes@suse.cz>

-- 
Miroslav

[PATCH v2 10/53] objtool/klp: Fix --debug-checksum for duplicate symbol names

[Josh Poimboeuf]

find_symbol_by_name() only returns the first match, so
--debug-checksum=<func> silently ignores any subsequent duplicately
named functions after the first.

Fix that, along with a new for_each_sym_by_name() helper.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/check.c               | 15 ++++++++++-----
 tools/objtool/include/objtool/elf.h |  5 +++++
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 9b11cf3193b9..e3604b1201f9 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3677,18 +3677,23 @@ static int checksum_debug_init(struct objtool_file *file)
 
 	s = dup;
 	while (*s) {
-		struct symbol *func;
+		bool found = false;
+		struct symbol *sym;
 		char *comma;
 
 		comma = strchr(s, ',');
 		if (comma)
 			*comma = '\0';
 
-		func = find_symbol_by_name(file->elf, s);
-		if (!func || !is_func_sym(func))
+		for_each_sym_by_name(file->elf, s, sym) {
+			if (!is_func_sym(sym))
+				continue;
+			sym->debug_checksum = 1;
+			found = true;
+		}
+
+		if (!found)
 			WARN("--debug-checksum: can't find '%s'", s);
-		else
-			func->debug_checksum = 1;
 
 		if (!comma)
 			break;
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index b142984eb9b5..00b04029023e 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -489,6 +489,11 @@ static inline void set_sym_next_reloc(struct reloc *reloc, struct reloc *next)
 #define for_each_sym_continue(elf, sym)					\
 	list_for_each_entry_continue(sym, &elf->symbols, global_list)
 
+#define for_each_sym_by_name(elf, _name, sym)				\
+	elf_hash_for_each_possible(elf, symbol_name, sym, name_hash,	\
+				   str_hash_demangled(_name))		\
+		if (strcmp(sym->name, _name)) {} else
+
 #define for_each_sym_by_demangled_name(elf, name, sym)			\
 	elf_hash_for_each_possible(elf, symbol_name, sym, name_hash,	\
 				   str_hash(name))			\
-- 
2.53.0

Re: [PATCH v2 10/53] objtool/klp: Fix --debug-checksum for duplicate symbol names

[Miroslav Benes]

On Thu, 30 Apr 2026 21:07:58 -0700, Josh Poimboeuf <jpoimboe@kernel.org> wrote:
> find_symbol_by_name() only returns the first match, so
> --debug-checksum=<func> silently ignores any subsequent duplicately
> named functions after the first.
> 
> Fix that, along with a new for_each_sym_by_name() helper.
> 
> 
> [...]

Reviewed-by: Miroslav Benes <mbenes@suse.cz>

-- 
Miroslav

[PATCH v2 11/53] objtool/klp: Fix handling of zero-length .altinstr_replacement sections

[Josh Poimboeuf]

When a section is empty (e.g. only zero-length alternative
replacements), there are no symbols to convert a section symbol
reference to.  Skip the reloc instead of erroring out.

Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 30ce234e01a1..a226e99948b3 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -1005,6 +1005,13 @@ static int convert_reloc_secsym_to_sym(struct elf *elf, struct reloc *reloc)
 	/* No dedicated section; find the symbol manually */
 	sym = find_symbol_containing(sec, arch_adjusted_addend(reloc));
 	if (!sym) {
+		/*
+		 * This is presumably an .altinstr_replacement section which is
+		 * empty due to it only having zero-length replacement(s).
+		 */
+		if (!sec_size(sec))
+			return 1;
+
 		/*
 		 * This can happen for special section references to weak code
 		 * whose symbol has been stripped by the linker.
@@ -1265,6 +1272,7 @@ static int clone_sym_relocs(struct elfs *e, struct symbol *patched_sym)
 
 	for_each_reloc(patched_rsec, patched_reloc) {
 		unsigned long offset;
+		int ret;
 
 		if (reloc_offset(patched_reloc) < start ||
 		    reloc_offset(patched_reloc) >= end)
@@ -1278,12 +1286,15 @@ static int clone_sym_relocs(struct elfs *e, struct symbol *patched_sym)
 		    !strcmp(patched_reloc->sym->sec->name, ".altinstr_aux"))
 			continue;
 
-		if (convert_reloc_sym(e->patched, patched_reloc)) {
+		ret = convert_reloc_sym(e->patched, patched_reloc);
+		if (ret < 0) {
 			ERROR_FUNC(patched_rsec->base, reloc_offset(patched_reloc),
 				   "failed to convert reloc sym '%s' to its proper format",
 				   patched_reloc->sym->name);
 			return -1;
 		}
+		if (ret > 0)
+			continue;
 
 		offset = out_sym->offset + (reloc_offset(patched_reloc) - patched_sym->offset);
 
-- 
2.53.0

[PATCH v2 12/53] objtool/klp: Fix cloning of zero-length section symbols

[Josh Poimboeuf]

Fix NULL dereference when cloning a symbol from an empty section.
sec->data is only populated for sections with non-zero size.

Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index a226e99948b3..17a6146b9406 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -681,7 +681,7 @@ static struct symbol *__clone_symbol(struct elf *elf, struct symbol *patched_sym
 			size_t size;
 
 			/* bss doesn't have data */
-			if (patched_sym->sec->data->d_buf)
+			if (patched_sym->sec->data && patched_sym->sec->data->d_buf)
 				data = patched_sym->sec->data->d_buf + patched_sym->offset;
 
 			if (is_sec_sym(patched_sym))
-- 
2.53.0

[PATCH v2 13/53] objtool/klp: Fix XXH3 state memory leak

[Josh Poimboeuf]

The XXH3 state allocated in checksum_init() is never freed.  Free it in
checksum_finish().

Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/include/objtool/checksum.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/objtool/include/objtool/checksum.h b/tools/objtool/include/objtool/checksum.h
index 7fe21608722a..0bd16fe9168b 100644
--- a/tools/objtool/include/objtool/checksum.h
+++ b/tools/objtool/include/objtool/checksum.h
@@ -26,6 +26,7 @@ static inline void checksum_finish(struct symbol *func)
 {
 	if (func && func->csum.state) {
 		func->csum.checksum = XXH3_64bits_digest(func->csum.state);
+		XXH3_freeState(func->csum.state);
 		func->csum.state = NULL;
 	}
 }
-- 
2.53.0

[PATCH v2 14/53] objtool/klp: Fix extraction of text annotations for alternatives

[Josh Poimboeuf]

Objtool is failing to extract text annotations which reference
.altinstr_replacement instructions:

  1) Alternative replacement fake symbols are NOTYPE rather than FUNC,
     and they don't have sym->included set, thus they aren't recognized
     by should_keep_special_sym().

  2) .discard.annotate_insn gets processed before .altinstr_replacement,
     so the referenced (fake) symbols don't have clones yet.

Fix the first issue by checking for a valid clone instead of
sym->included and by accepting NOTYPE symbols when processing
.discard.annotate_insn.

Fix the second issue by deferring text annotation processing until after
the other special sections have been cloned.

Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 33 ++++++++++++++++++++++++++++-----
 1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 17a6146b9406..42970b38728f 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -1437,6 +1437,7 @@ static int create_fake_symbols(struct elf *elf)
 /* Keep a special section entry if it references an included function */
 static bool should_keep_special_sym(struct elf *elf, struct symbol *sym)
 {
+	bool annotate_insn = !strcmp(sym->sec->name, ".discard.annotate_insn");
 	struct reloc *reloc;
 
 	if (is_sec_sym(sym) || !sym->sec->rsec)
@@ -1446,7 +1447,16 @@ static bool should_keep_special_sym(struct elf *elf, struct symbol *sym)
 		if (convert_reloc_sym(elf, reloc))
 			continue;
 
-		if (is_func_sym(reloc->sym) && reloc->sym->included)
+		if (!reloc->sym->clone || is_undef_sym(reloc->sym->clone))
+			continue;
+
+		/*
+		 * Keep special section references to cloned functions.
+		 * In some cases annotate_insn can also reference cloned alt
+		 * replacement fake symbols; keep those references as well.
+		 */
+		if (is_func_sym(reloc->sym) ||
+		    (annotate_insn && is_notype_sym(reloc->sym)))
 			return true;
 	}
 
@@ -1590,15 +1600,28 @@ static int clone_special_section(struct elfs *e, struct section *patched_sec)
 /* Extract only the needed bits from special sections */
 static int clone_special_sections(struct elfs *e)
 {
-	struct section *patched_sec;
+	struct section *sec, *annotate_insn = NULL;
 
-	for_each_sec(e->patched, patched_sec) {
-		if (is_special_section(patched_sec)) {
-			if (clone_special_section(e, patched_sec))
+	for_each_sec(e->patched, sec) {
+		if (is_special_section(sec)) {
+			if (!strcmp(sec->name, ".discard.annotate_insn")) {
+				annotate_insn = sec;
+				continue;
+			}
+			if (clone_special_section(e, sec))
 				return -1;
 		}
 	}
 
+	/*
+	 * Do .discard.annotate_insn last, it can reference other special
+	 * sections (alt replacements) so they need to be cloned first.
+	 */
+	if (annotate_insn) {
+		if (clone_special_section(e, annotate_insn))
+			return -1;
+	}
+
 	return 0;
 }
 
-- 
2.53.0

[PATCH v2 15/53] objtool/klp: Fix kCFI trap handling

[Josh Poimboeuf]

.kcfi_traps contains references to kCFI trap instruction locations.
When a KCFI type check fails at an indirect call, the trap handler looks
up the faulting address in this section.

Add it to the special sections list so the entries get extracted for the
changed functions they reference.

Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 42970b38728f..dd0e51dfc621 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -291,6 +291,7 @@ static bool is_special_section(struct section *sec)
 {
 	static const char * const specials[] = {
 		".altinstructions",
+		".kcfi_traps",
 		".smp_locks",
 		"__bug_table",
 		"__ex_table",
-- 
2.53.0

[PATCH v2 16/53] objtool/klp: Fix relocation conversion failures for R_X86_64_NONE

[Josh Poimboeuf]

Objtool has some hacks which NOP out certain calls/jumps and replace
their relocations with R_X86_64_NONE.  The klp-diff relocation
extraction code will error out when trying to copy these relocations due
to their negative addend, which would only makes sense for a PC-relative
branch instruction.  Just ignore them.

Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index dd0e51dfc621..19bc811db396 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -1033,6 +1033,9 @@ static int convert_reloc_secsym_to_sym(struct elf *elf, struct reloc *reloc)
  */
 static int convert_reloc_sym(struct elf *elf, struct reloc *reloc)
 {
+	if (reloc_type(reloc) == R_NONE)
+		return 1;
+
 	if (is_reloc_allowed(reloc))
 		return 0;
 
-- 
2.53.0

[PATCH v2 17/53] objtool: Move mark_rodata() to elf.c

[Josh Poimboeuf]

Move the sec->rodata marking from check.c to elf.c so it's set during
ELF reading rather than during the check pipeline.  This makes the
rodata flag available to all objtool users, including klp-diff which
reads ELF files directly without running check().

Add an is_rodata_sec() helper to elf.h for consistency with
is_text_sec() and is_string_sec().

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/check.c               | 11 +++--------
 tools/objtool/elf.c                 | 13 +++++++++++++
 tools/objtool/include/objtool/elf.h |  5 +++++
 3 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index e3604b1201f9..e7579c4e46dc 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2566,7 +2566,6 @@ static int classify_symbols(struct objtool_file *file)
 static void mark_rodata(struct objtool_file *file)
 {
 	struct section *sec;
-	bool found = false;
 
 	/*
 	 * Search for the following rodata sections, each of which can
@@ -2579,15 +2578,11 @@ static void mark_rodata(struct objtool_file *file)
 	 * .rodata.str1.* sections are ignored; they don't contain jump tables.
 	 */
 	for_each_sec(file->elf, sec) {
-		if ((!strncmp(sec->name, ".rodata", 7) &&
-		     !strstr(sec->name, ".str1.")) ||
-		    !strncmp(sec->name, ".data.rel.ro", 12)) {
-			sec->rodata = true;
-			found = true;
+		if (is_rodata_sec(sec)) {
+			file->rodata = true;
+			return;
 		}
 	}
-
-	file->rodata = found;
 }
 
 static void mark_holes(struct objtool_file *file)
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index dc39132f71c1..87c6e00749c6 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -1138,6 +1138,17 @@ static int read_relocs(struct elf *elf)
 	return 0;
 }
 
+static void mark_rodata(struct elf *elf)
+{
+	struct section *sec;
+
+	for_each_sec(elf, sec) {
+		if ((strstarts(sec->name, ".rodata") && !strstr(sec->name, ".str1.")) ||
+		    strstarts(sec->name, ".data.rel.ro"))
+			sec->rodata = true;
+	}
+}
+
 struct elf *elf_open_read(const char *name, int flags)
 {
 	struct elf *elf;
@@ -1188,6 +1199,8 @@ struct elf *elf_open_read(const char *name, int flags)
 	if (read_sections(elf))
 		goto err;
 
+	mark_rodata(elf);
+
 	if (read_symbols(elf))
 		goto err;
 
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index 00b04029023e..ab5f7017ec34 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -317,6 +317,11 @@ static inline bool is_text_sec(struct section *sec)
 	return sec->sh.sh_flags & SHF_EXECINSTR;
 }
 
+static inline bool is_rodata_sec(struct section *sec)
+{
+	return sec->rodata;
+}
+
 static inline bool sec_changed(struct section *sec)
 {
 	return sec->_changed;
-- 
2.53.0

[PATCH v2 18/53] objtool/klp: Simplify reloc symbol conversion

[Josh Poimboeuf]

Inline section_reference_needed() and is_reloc_allowed() into
convert_reloc_sym() and remove the redundant is_reloc_allowed() check in
clone_reloc().

Move the is_sec_sym() checks into the convert callees so they become
no-ops when the reloc is already in the right format.  This allows
convert_reloc_sym() to unconditionally dispatch to the right converter
based on section type.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 76 +++++++++++++++-------------------------
 1 file changed, 28 insertions(+), 48 deletions(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 19bc811db396..78633c9b68eb 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -838,39 +838,6 @@ static int clone_included_functions(struct elfs *e)
 	return 0;
 }
 
-/*
- * Determine whether a relocation should reference the section rather than the
- * underlying symbol.
- */
-static bool section_reference_needed(struct section *sec)
-{
-	/*
-	 * String symbols are zero-length and uncorrelated.  It's easier to
-	 * deal with them as section symbols.
-	 */
-	if (is_string_sec(sec))
-		return true;
-
-	/*
-	 * .rodata has mostly anonymous data so there's no way to determine the
-	 * length of a needed reference.  just copy the whole section if needed.
-	 */
-	if (strstarts(sec->name, ".rodata"))
-		return true;
-
-	/* UBSAN anonymous data */
-	if (strstarts(sec->name, ".data..Lubsan") ||	/* GCC */
-	    strstarts(sec->name, ".data..L__unnamed_"))	/* Clang */
-		return true;
-
-	return false;
-}
-
-static bool is_reloc_allowed(struct reloc *reloc)
-{
-	return section_reference_needed(reloc->sym->sec) == is_sec_sym(reloc->sym);
-}
-
 static struct export *find_export(struct symbol *sym)
 {
 	struct export *export;
@@ -979,11 +946,15 @@ static bool klp_reloc_needed(struct reloc *patched_reloc)
 	return true;
 }
 
+/* Return -1 error, 0 success, 1 skip */
 static int convert_reloc_sym_to_secsym(struct elf *elf, struct reloc *reloc)
 {
 	struct symbol *sym = reloc->sym;
 	struct section *sec = sym->sec;
 
+	if (is_sec_sym(sym))
+		return 0;
+
 	if (!sec->sym && !elf_create_section_symbol(elf, sec))
 		return -1;
 
@@ -993,11 +964,15 @@ static int convert_reloc_sym_to_secsym(struct elf *elf, struct reloc *reloc)
 	return 0;
 }
 
+/* Return -1 error, 0 success, 1 skip */
 static int convert_reloc_secsym_to_sym(struct elf *elf, struct reloc *reloc)
 {
 	struct symbol *sym = reloc->sym;
 	struct section *sec = sym->sec;
 
+	if (!is_sec_sym(sym))
+		return 0;
+
 	/* If the symbol has a dedicated section, it's easy to find */
 	sym = find_symbol_by_offset(sec, 0);
 	if (sym && sym->len == sec_size(sec))
@@ -1027,22 +1002,34 @@ static int convert_reloc_secsym_to_sym(struct elf *elf, struct reloc *reloc)
 	return 0;
 }
 
+/*
+ * Sections with anonymous or uncorrelated data (strings, UBSAN data)
+ * need section symbol references.
+ */
+static bool is_uncorrelated_section(struct section *sec)
+{
+	return is_string_sec(sec) ||
+	       strstarts(sec->name, ".rodata") ||
+	       strstarts(sec->name, ".data..Lubsan") ||		/* GCC */
+	       strstarts(sec->name, ".data..L__unnamed_");	/* Clang */
+}
+
 /*
  * Convert a relocation symbol reference to the needed format: either a section
- * symbol or the underlying symbol itself.
+ * symbol or the underlying symbol itself.  Return -1 error, 0 success, 1 skip.
  */
 static int convert_reloc_sym(struct elf *elf, struct reloc *reloc)
 {
+	struct section *sec = reloc->sym->sec;
+
 	if (reloc_type(reloc) == R_NONE)
 		return 1;
 
-	if (is_reloc_allowed(reloc))
-		return 0;
-
-	if (section_reference_needed(reloc->sym->sec))
+	if (is_uncorrelated_section(sec))
 		return convert_reloc_sym_to_secsym(elf, reloc);
-	else
-		return convert_reloc_secsym_to_sym(elf, reloc);
+
+	/* Everything else: references should use named symbols. */
+	return convert_reloc_secsym_to_sym(elf, reloc);
 }
 
 /*
@@ -1187,13 +1174,6 @@ static int clone_reloc(struct elfs *e, struct reloc *patched_reloc,
 	struct symbol *out_sym;
 	bool klp;
 
-	if (!is_reloc_allowed(patched_reloc)) {
-		ERROR_FUNC(patched_reloc->sec->base, reloc_offset(patched_reloc),
-			   "missing symbol for reference to %s+%ld",
-			   patched_sym->name, addend);
-		return -1;
-	}
-
 	klp = klp_reloc_needed(patched_reloc);
 
 	dbg_clone_reloc(sec, offset, patched_sym, addend, export, klp);
@@ -1223,7 +1203,7 @@ static int clone_reloc(struct elfs *e, struct reloc *patched_reloc,
 
 	/*
 	 * For strings, all references use section symbols, thanks to
-	 * section_reference_needed().  clone_symbol() has cloned an empty
+	 * convert_reloc_sym().  clone_symbol() has cloned an empty
 	 * version of the string section.  Now copy the string itself.
 	 */
 	if (is_string_sec(patched_sym->sec)) {
-- 
2.53.0

Re: [PATCH v2 18/53] objtool/klp: Simplify reloc symbol conversion

[Song Liu]

On Fri, May 1, 2026 at 5:09 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> Inline section_reference_needed() and is_reloc_allowed() into
> convert_reloc_sym() and remove the redundant is_reloc_allowed() check in
> clone_reloc().
>
> Move the is_sec_sym() checks into the convert callees so they become
> no-ops when the reloc is already in the right format.  This allows
> convert_reloc_sym() to unconditionally dispatch to the right converter
> based on section type.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

Re: [PATCH v2 18/53] objtool/klp: Simplify reloc symbol conversion

[Miroslav Benes]

On Thu, 30 Apr 2026 21:08:06 -0700, Josh Poimboeuf <jpoimboe@kernel.org> wrote:
> Inline section_reference_needed() and is_reloc_allowed() into
> convert_reloc_sym() and remove the redundant is_reloc_allowed() check in
> clone_reloc().
> 
> Move the is_sec_sym() checks into the convert callees so they become
> no-ops when the reloc is already in the right format.  This allows
> convert_reloc_sym() to unconditionally dispatch to the right converter
> based on section type.
> 
> [...]

Reviewed-by: Miroslav Benes <mbenes@suse.cz>

-- 
Miroslav

[PATCH v2 19/53] objtool/klp: Fix pointer comparisons for rodata objects

[Josh Poimboeuf]

klp-diff treats all rodata as uncorrelated, so any reference to it uses
a duplicated copy rather than using a KLP reloc.

For the contents of the data itself, a duplicated copy is fine.
However, pointer comparisons (e.g., f->f_op == &foo_ops) are broken.

Fix it by correlating non-anonymous rodata objects.

Also, use a new find_symbol_containing_inclusive() helper for matching
the end of a symbol so bounds calculations don't get broken, for the
case where an array or other symbol's ending address is used as part of
a bounds calculation.

While these are really two distinct changes, they need to be done in the
same patch so as to avoid introducing bisection regressions.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/elf.c                 | 14 ++++++++++++++
 tools/objtool/include/objtool/elf.h |  1 +
 tools/objtool/klp-diff.c            | 15 +++++++++++++--
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 87c6e00749c6..5a20dab683dd 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -207,6 +207,20 @@ struct symbol *find_symbol_containing(const struct section *sec, unsigned long o
 	return sym ? sym->alias : NULL;
 }
 
+/*
+ * Also match the symbol end address which can be used for a bounds comparison.
+ */
+struct symbol *find_symbol_containing_inclusive(const struct section *sec,
+						unsigned long offset)
+{
+	struct symbol *sym = find_symbol_containing(sec, offset);
+
+	if (!sym && offset)
+		sym = find_symbol_containing(sec, offset - 1);
+
+	return sym;
+}
+
 /*
  * Returns size of hole starting at @offset.
  */
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index ab5f7017ec34..8a543cea43b9 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -211,6 +211,7 @@ struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset);
 struct symbol *find_symbol_by_name(const struct elf *elf, const char *name);
 struct symbol *find_global_symbol_by_name(const struct elf *elf, const char *name);
 struct symbol *find_symbol_containing(const struct section *sec, unsigned long offset);
+struct symbol *find_symbol_containing_inclusive(const struct section *sec, unsigned long offset);
 int find_symbol_hole_containing(const struct section *sec, unsigned long offset);
 struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset);
 struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 78633c9b68eb..bf37c652188b 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -386,6 +386,7 @@ static bool dont_correlate(struct symbol *sym)
 	       is_uncorrelated_static_local(sym) ||
 	       is_local_label(sym) ||
 	       is_string_sec(sym->sec) ||
+	       (is_rodata_sec(sym->sec) && !is_object_sym(sym)) ||
 	       is_initcall_sym(sym) ||
 	       is_addressable_sym(sym) ||
 	       is_special_section(sym->sec) ||
@@ -979,7 +980,7 @@ static int convert_reloc_secsym_to_sym(struct elf *elf, struct reloc *reloc)
 		goto found_sym;
 
 	/* No dedicated section; find the symbol manually */
-	sym = find_symbol_containing(sec, arch_adjusted_addend(reloc));
+	sym = find_symbol_containing_inclusive(sec, arch_adjusted_addend(reloc));
 	if (!sym) {
 		/*
 		 * This is presumably an .altinstr_replacement section which is
@@ -988,6 +989,17 @@ static int convert_reloc_secsym_to_sym(struct elf *elf, struct reloc *reloc)
 		if (!sec_size(sec))
 			return 1;
 
+		/*
+		 * .rodata is a mixed bag of named objects and anonymous data.
+		 *
+		 * Convert section symbol references to named object symbols
+		 * when possible, to preserve pointer identity for const
+		 * structs like file_operations.  Otherwise a section symbol is
+		 * fine.
+		 */
+		if (is_rodata_sec(sec))
+			return 0;
+
 		/*
 		 * This can happen for special section references to weak code
 		 * whose symbol has been stripped by the linker.
@@ -1009,7 +1021,6 @@ static int convert_reloc_secsym_to_sym(struct elf *elf, struct reloc *reloc)
 static bool is_uncorrelated_section(struct section *sec)
 {
 	return is_string_sec(sec) ||
-	       strstarts(sec->name, ".rodata") ||
 	       strstarts(sec->name, ".data..Lubsan") ||		/* GCC */
 	       strstarts(sec->name, ".data..L__unnamed_");	/* Clang */
 }
-- 
2.53.0

Re: [PATCH v2 19/53] objtool/klp: Fix pointer comparisons for rodata objects

[Song Liu]

On Fri, May 1, 2026 at 5:08 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> klp-diff treats all rodata as uncorrelated, so any reference to it uses
> a duplicated copy rather than using a KLP reloc.
>
> For the contents of the data itself, a duplicated copy is fine.
> However, pointer comparisons (e.g., f->f_op == &foo_ops) are broken.
>
> Fix it by correlating non-anonymous rodata objects.
>
> Also, use a new find_symbol_containing_inclusive() helper for matching
> the end of a symbol so bounds calculations don't get broken, for the
> case where an array or other symbol's ending address is used as part of
> a bounds calculation.
>
> While these are really two distinct changes, they need to be done in the
> same patch so as to avoid introducing bisection regressions.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

[PATCH v2 20/53] objtool/klp: Don't correlate .rodata.cst* constant pool objects

[Josh Poimboeuf]

Clang aggregates UBSAN type descriptors into shared anonymous
.data..L__unnamed_* sections.  This data is used by UBSAN trap handlers.

When a changed function has an UBSAN bounds check, klp-diff clones the
entire UBSAN data section associated with the TU.  Relocations within
the cloned section that reference named rodata objects in .rodata.cst*
(like 'exponent', 'pirq_ali_set.irqmap') become KLP relocations because
those objects now get correlated.

That results in a .klp.rela.vmlinux..data section which can easily have
thousands of KLP relocs, most of which are completely superfluous, used
by functions which aren't cloned to the patch module.

The .rodata.cst* sections are SHF_MERGE constant pool sections
containing small fixed-size data (lookup tables, bitmasks) that is only
read by value.  Pointer identity is never relevant for these objects, so
correlating them is unnecessary.

Exclude .rodata.cst* objects from correlation so they get cloned as
local data instead of generating KLP relocations.

It might be possible to someday treat UBSAN data sections as special
sections, and only extract the few needed entries.  But this works for
now.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index bf37c652188b..ca87bcb9afa3 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -372,6 +372,21 @@ static bool is_initcall_sym(struct symbol *sym)
 	       strstarts(sym->name, "__initstub__");
 }
 
+/*
+ * Some .rodata is anonymous and can't be correlated due to there being no
+ * symbol names.
+ *
+ * The .rodata.cst* sections aren't technically anonymous, they're SHF_MERGE
+ * constant pool sections containing small fixed-size data (lookup tables,
+ * bitmasks) which are only read by value, so pointer equivalence isn't needed.
+ * They are typically referenced by UBSAN data sections.
+ */
+static bool is_anonymous_rodata(struct symbol *sym)
+{
+	return is_rodata_sec(sym->sec) &&
+	       (!is_object_sym(sym) || strstarts(sym->sec->name, ".rodata.cst"));
+}
+
 /*
  * These symbols should never be correlated, so their local patched versions
  * are used instead of linking to the originals.
@@ -386,7 +401,7 @@ static bool dont_correlate(struct symbol *sym)
 	       is_uncorrelated_static_local(sym) ||
 	       is_local_label(sym) ||
 	       is_string_sec(sym->sec) ||
-	       (is_rodata_sec(sym->sec) && !is_object_sym(sym)) ||
+	       is_anonymous_rodata(sym) ||
 	       is_initcall_sym(sym) ||
 	       is_addressable_sym(sym) ||
 	       is_special_section(sym->sec) ||
-- 
2.53.0

Re: [PATCH v2 20/53] objtool/klp: Don't correlate .rodata.cst* constant pool objects

[Song Liu]

On Fri, May 1, 2026 at 5:08 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> Clang aggregates UBSAN type descriptors into shared anonymous
> .data..L__unnamed_* sections.  This data is used by UBSAN trap handlers.
>
> When a changed function has an UBSAN bounds check, klp-diff clones the
> entire UBSAN data section associated with the TU.  Relocations within
> the cloned section that reference named rodata objects in .rodata.cst*
> (like 'exponent', 'pirq_ali_set.irqmap') become KLP relocations because
> those objects now get correlated.
>
> That results in a .klp.rela.vmlinux..data section which can easily have
> thousands of KLP relocs, most of which are completely superfluous, used
> by functions which aren't cloned to the patch module.
>
> The .rodata.cst* sections are SHF_MERGE constant pool sections
> containing small fixed-size data (lookup tables, bitmasks) that is only
> read by value.  Pointer identity is never relevant for these objects, so
> correlating them is unnecessary.
>
> Exclude .rodata.cst* objects from correlation so they get cloned as
> local data instead of generating KLP relocations.
>
> It might be possible to someday treat UBSAN data sections as special
> sections, and only extract the few needed entries.  But this works for
> now.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
> ---
>  tools/objtool/klp-diff.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
> index bf37c652188b..ca87bcb9afa3 100644
> --- a/tools/objtool/klp-diff.c
> +++ b/tools/objtool/klp-diff.c
> @@ -372,6 +372,21 @@ static bool is_initcall_sym(struct symbol *sym)
>                strstarts(sym->name, "__initstub__");
>  }
>
> +/*
> + * Some .rodata is anonymous and can't be correlated due to there being no
> + * symbol names.
> + *
> + * The .rodata.cst* sections aren't technically anonymous, they're SHF_MERGE
> + * constant pool sections containing small fixed-size data (lookup tables,
> + * bitmasks) which are only read by value, so pointer equivalence isn't needed.
> + * They are typically referenced by UBSAN data sections.
> + */
> +static bool is_anonymous_rodata(struct symbol *sym)
> +{
> +       return is_rodata_sec(sym->sec) &&
> +              (!is_object_sym(sym) || strstarts(sym->sec->name, ".rodata.cst"));
> +}
> +
>  /*
>   * These symbols should never be correlated, so their local patched versions
>   * are used instead of linking to the originals.
> @@ -386,7 +401,7 @@ static bool dont_correlate(struct symbol *sym)
>                is_uncorrelated_static_local(sym) ||
>                is_local_label(sym) ||
>                is_string_sec(sym->sec) ||
> -              (is_rodata_sec(sym->sec) && !is_object_sym(sym)) ||
^^^^
This line was added in 19/53. Maybe we can merge 19 and 20?

Thanks,
Song

> +              is_anonymous_rodata(sym) ||
>                is_initcall_sym(sym) ||
>                is_addressable_sym(sym) ||
>                is_special_section(sym->sec) ||
> --
> 2.53.0
>

Re: [PATCH v2 20/53] objtool/klp: Don't correlate .rodata.cst* constant pool objects

[Josh Poimboeuf]

On Fri, May 01, 2026 at 11:37:49AM +0100, Song Liu wrote:
> > +/*
> > + * Some .rodata is anonymous and can't be correlated due to there being no
> > + * symbol names.
> > + *
> > + * The .rodata.cst* sections aren't technically anonymous, they're SHF_MERGE
> > + * constant pool sections containing small fixed-size data (lookup tables,
> > + * bitmasks) which are only read by value, so pointer equivalence isn't needed.
> > + * They are typically referenced by UBSAN data sections.
> > + */
> > +static bool is_anonymous_rodata(struct symbol *sym)
> > +{
> > +       return is_rodata_sec(sym->sec) &&
> > +              (!is_object_sym(sym) || strstarts(sym->sec->name, ".rodata.cst"));
> > +}
> > +
> >  /*
> >   * These symbols should never be correlated, so their local patched versions
> >   * are used instead of linking to the originals.
> > @@ -386,7 +401,7 @@ static bool dont_correlate(struct symbol *sym)
> >                is_uncorrelated_static_local(sym) ||
> >                is_local_label(sym) ||
> >                is_string_sec(sym->sec) ||
> > -              (is_rodata_sec(sym->sec) && !is_object_sym(sym)) ||
> ^^^^
> This line was added in 19/53. Maybe we can merge 19 and 20?

I think I'd prefer to keep them separate as they are two distinct issues
related to rodata: pointer equivalence (patch 19) and UBSAN mergeable
constants (patch 20).

-- 
Josh

Re: [PATCH v2 20/53] objtool/klp: Don't correlate .rodata.cst* constant pool objects

[Song Liu]

On Fri, May 1, 2026 at 6:04 PM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> On Fri, May 01, 2026 at 11:37:49AM +0100, Song Liu wrote:
> > > +/*
> > > + * Some .rodata is anonymous and can't be correlated due to there being no
> > > + * symbol names.
> > > + *
> > > + * The .rodata.cst* sections aren't technically anonymous, they're SHF_MERGE
> > > + * constant pool sections containing small fixed-size data (lookup tables,
> > > + * bitmasks) which are only read by value, so pointer equivalence isn't needed.
> > > + * They are typically referenced by UBSAN data sections.
> > > + */
> > > +static bool is_anonymous_rodata(struct symbol *sym)
> > > +{
> > > +       return is_rodata_sec(sym->sec) &&
> > > +              (!is_object_sym(sym) || strstarts(sym->sec->name, ".rodata.cst"));
> > > +}
> > > +
> > >  /*
> > >   * These symbols should never be correlated, so their local patched versions
> > >   * are used instead of linking to the originals.
> > > @@ -386,7 +401,7 @@ static bool dont_correlate(struct symbol *sym)
> > >                is_uncorrelated_static_local(sym) ||
> > >                is_local_label(sym) ||
> > >                is_string_sec(sym->sec) ||
> > > -              (is_rodata_sec(sym->sec) && !is_object_sym(sym)) ||
> > ^^^^
> > This line was added in 19/53. Maybe we can merge 19 and 20?
>
> I think I'd prefer to keep them separate as they are two distinct issues
> related to rodata: pointer equivalence (patch 19) and UBSAN mergeable
> constants (patch 20).

Fair enough. I think we can keep these two patches as-is.

Thanks,
Song

Acked-by: Song Liu <song@kernel.org>

[PATCH v2 21/53] objtool/klp: Fix reloc corruption in convert_reloc_sym_to_secsym()

[Josh Poimboeuf]

Use the section symbol's index instead of the old symbol's index when
updating the ELF relocation entry in convert_reloc_sym_to_secsym().

Found by Sashiko review.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index ca87bcb9afa3..463b6daa5234 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -975,7 +975,7 @@ static int convert_reloc_sym_to_secsym(struct elf *elf, struct reloc *reloc)
 		return -1;
 
 	reloc->sym = sec->sym;
-	set_reloc_sym(elf, reloc, sym->idx);
+	set_reloc_sym(elf, reloc, sec->sym->idx);
 	set_reloc_addend(elf, reloc, sym->offset + reloc_addend(reloc));
 	return 0;
 }
-- 
2.53.0

Re: [PATCH v2 21/53] objtool/klp: Fix reloc corruption in convert_reloc_sym_to_secsym()

[Song Liu]

On Fri, May 1, 2026 at 5:10 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> Use the section symbol's index instead of the old symbol's index when
> updating the ELF relocation entry in convert_reloc_sym_to_secsym().
>
> Found by Sashiko review.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

[PATCH v2 22/53] objtool: Fix reloc hash collision in find_reloc_by_dest_range()

[Josh Poimboeuf]

In find_reloc_by_dest_range(), hash collisions can cause a high-offset
relocation to appear when probing a low-offset hash bucket.

Only return early when the best match found so far genuinely belongs to
the current bucket (its offset is within the bucket's stride range).
Otherwise, continue scanning later buckets which may contain
lower-offset matches.

This ensures the first reloc in the range gets returned.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Fixes: 74b873e49d92 ("objtool: Optimize find_rela_by_dest_range()")
Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/elf.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 5a20dab683dd..f41280e454ca 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -315,8 +315,9 @@ struct symbol *find_global_symbol_by_name(const struct elf *elf, const char *nam
 	return NULL;
 }
 
+/* If there are multiple matches, return the first one in the range */
 struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *sec,
-				     unsigned long offset, unsigned int len)
+				       unsigned long offset, unsigned int len)
 {
 	struct reloc *reloc, *r = NULL;
 	struct section *rsec;
@@ -338,11 +339,11 @@ struct reloc *find_reloc_by_dest_range(const struct elf *elf, struct section *se
 					r = reloc;
 			}
 		}
-		if (r)
+		if (r && (reloc_offset(r) & OFFSET_STRIDE_MASK) == o)
 			return r;
 	}
 
-	return NULL;
+	return r;
 }
 
 struct reloc *find_reloc_by_dest(const struct elf *elf, struct section *sec, unsigned long offset)
-- 
2.53.0

[PATCH v2 23/53] klp-build: Fix hang on out-of-date .config

[Josh Poimboeuf]

If .config is out of date with the kernel source, 'make syncconfig'
hangs while waiting for user input on new config options.  Detect the
mismatch and return an error.

Fixes: 6f93f7b06810 ("livepatch/klp-build: Fix inconsistent kernel version")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 scripts/livepatch/klp-build | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index 0ad7e6631314..e19d93b78fcb 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -306,7 +306,12 @@ set_kernelversion() {
 
 	stash_file "$file"
 
-	kernelrelease="$(cd "$SRC" && make syncconfig &>/dev/null && make -s kernelrelease)"
+	if [[ -n "$(make -s listnewconfig 2>/dev/null)" ]]; then
+		die ".config mismatch, check your .config or run 'make olddefconfig'"
+	fi
+	make syncconfig &>/dev/null || die "make syncconfig failed"
+
+	kernelrelease="$(make -s kernelrelease)"
 	[[ -z "$kernelrelease" ]] && die "failed to get kernel version"
 
 	sed -i "2i echo $kernelrelease; exit 0" scripts/setlocalversion
-- 
2.53.0

Re: [PATCH v2 23/53] klp-build: Fix hang on out-of-date .config

[Song Liu]

On Fri, May 1, 2026 at 5:10 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> If .config is out of date with the kernel source, 'make syncconfig'
> hangs while waiting for user input on new config options.  Detect the
> mismatch and return an error.
>
> Fixes: 6f93f7b06810 ("livepatch/klp-build: Fix inconsistent kernel version")
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

[PATCH v2 24/53] klp-build: Fix checksum comparison for changed offsets

[Josh Poimboeuf]

The klp-build -f/--show-first-changed feature uses diff to compare
checksum log lines between original and patched objects.  However, diff
compares entire lines, including the offset field.  When a function is
at a different section offset, the offset field differs even though the
instruction checksum is identical, causing the wrong instruction to be
printed.

Only compare the checksum field when looking for the first changed
instruction.  Also print both the original and patched offsets when they
differ.

Fixes: 78be9facfb5e ("livepatch/klp-build: Add --show-first-changed option to show function divergence")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 scripts/livepatch/klp-build | 30 +++++++++++++++++++++++-------
 1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index e19d93b78fcb..8f0ea56f2640 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -727,13 +727,29 @@ diff_checksums() {
 		)
 
 		for func in ${funcs[$file]}; do
-			diff <( grep0 -E "^DEBUG: .*checksum: $func " "$orig_log"    | sed "s|$ORIG_DIR/||")	\
-			     <( grep0 -E "^DEBUG: .*checksum: $func " "$patched_log" | sed "s|$PATCHED_DIR/||")	\
-				| gawk '/^< DEBUG: / {
-					gsub(/:/, "")
-					printf "%s: %s: %s\n", $3, $5, $6
-					exit
-			}' || true
+			local -a orig patched
+			paste <(grep0 -E "^DEBUG: .*checksum: $func " "$orig_log") \
+			      <(grep0 -E "^DEBUG: .*checksum: $func " "$patched_log") |
+			while IFS= read -r line; do
+				read -ra orig <<< "${line%%$'\t'*}"
+				read -ra patched <<< "${line#*$'\t'}"
+
+				if [[ ${#patched[@]} -eq 0 ]]; then
+					printf "%s: %s: %s (removed)\n" "${orig[1]%:}" "${orig[3]}" "${orig[-2]}"
+					break
+				elif [[ ${#orig[@]} -eq 0 ]]; then
+					printf "%s: %s: %s (added)\n" "${patched[1]%:}" "${patched[3]}" "${patched[-2]}"
+					break
+				fi
+
+				[[ "${orig[-1]}" == "${patched[-1]}" ]] && continue
+
+				printf "%s: %s: %s" "${orig[1]%:}" "${orig[3]}" "${orig[-2]}"
+				[[ "${orig[-2]}" != "${patched[-2]}" ]] && \
+					printf " (patched: %s)" "${patched[-2]}"
+				printf "\n"
+				break
+			done || true
 		done
 	done
 }
-- 
2.53.0

Re: [PATCH v2 24/53] klp-build: Fix checksum comparison for changed offsets

[Song Liu]

On Fri, May 1, 2026 at 5:09 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> The klp-build -f/--show-first-changed feature uses diff to compare
> checksum log lines between original and patched objects.  However, diff
> compares entire lines, including the offset field.  When a function is
> at a different section offset, the offset field differs even though the
> instruction checksum is identical, causing the wrong instruction to be
> printed.
>
> Only compare the checksum field when looking for the first changed
> instruction.  Also print both the original and patched offsets when they
> differ.
>
> Fixes: 78be9facfb5e ("livepatch/klp-build: Add --show-first-changed option to show function divergence")
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

[PATCH v2 25/53] klp-build: Don't use errexit

[Josh Poimboeuf]

The errtrace option (combined with the ERR trap) already serves the same
function (and more) as errexit, so errexit is redundant.  And it has
more pitfalls.  Remove it.

Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 scripts/livepatch/klp-build | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index 8f0ea56f2640..68d61b72f39a 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -3,7 +3,7 @@
 #
 # Build a livepatch module
 
-# shellcheck disable=SC1090,SC2155
+# shellcheck disable=SC1090,SC2155,SC2164
 
 if (( BASH_VERSINFO[0]  < 4 || \
      (BASH_VERSINFO[0] == 4 && BASH_VERSINFO[1] < 4) )); then
@@ -11,13 +11,12 @@ if (( BASH_VERSINFO[0]  < 4 || \
 	exit 1
 fi
 
-set -o errexit
 set -o errtrace
 set -o pipefail
 set -o nounset
 
 # Allow doing 'cmd | mapfile -t array' instead of 'mapfile -t array < <(cmd)'.
-# This helps keep execution in pipes so pipefail+errexit can catch errors.
+# This helps keep execution in pipes so pipefail+ERR trap can catch errors.
 shopt -s lastpipe
 
 unset DEBUG_CLONE DIFF_CHECKSUM SKIP_CLEANUP XTRACE
-- 
2.53.0

[PATCH v2 26/53] klp-build: Validate patch file existence

[Josh Poimboeuf]

Make sure all patch files actually exist.  Otherwise there can be
confusing errors later.

Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 scripts/livepatch/klp-build | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index 68d61b72f39a..13709d20e295 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -157,6 +157,7 @@ process_args() {
 	local short
 	local long
 	local args
+	local patch
 
 	short="hfj:o:vdS:T"
 	long="help,show-first-changed,jobs:,output:,no-replace,verbose,debug,short-circuit:,keep-tmp"
@@ -235,6 +236,10 @@ process_args() {
 
 	KEEP_TMP="$keep_tmp"
 	PATCHES=("$@")
+
+	for patch in "${PATCHES[@]}"; do
+		[[ -f "$patch" ]] || die "$patch doesn't exist"
+	done
 }
 
 # temporarily disable xtrace for especially verbose code
-- 
2.53.0

[PATCH v2 27/53] klp-build: Suppress excessive fuzz output by default

[Josh Poimboeuf]

When a patch applies with fuzz, the detailed output from the patch tool
can be very noisy, especially for big patches.

Suppress the fuzz details by default, while keeping the "applied with
fuzz" warning.  The noise can be restored with '--verbose'.

Acked-by: Song Liu <song@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 scripts/livepatch/klp-build | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index 13709d20e295..dc2c5c33d1db 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -19,12 +19,11 @@ set -o nounset
 # This helps keep execution in pipes so pipefail+ERR trap can catch errors.
 shopt -s lastpipe
 
-unset DEBUG_CLONE DIFF_CHECKSUM SKIP_CLEANUP XTRACE
+unset DEBUG_CLONE DIFF_CHECKSUM SKIP_CLEANUP VERBOSE XTRACE
 
 REPLACE=1
 SHORT_CIRCUIT=0
 JOBS="$(getconf _NPROCESSORS_ONLN)"
-VERBOSE="-s"
 shopt -o xtrace | grep -q 'on' && XTRACE=1
 
 # Avoid removing the previous $TMP_DIR until args have been fully processed.
@@ -194,7 +193,7 @@ process_args() {
 				shift
 				;;
 			-v | --verbose)
-				VERBOSE="V=1"
+				VERBOSE=1
 				shift
 				;;
 			-d | --debug)
@@ -381,7 +380,7 @@ apply_patch() {
 		echo "$output" >&2
 		die "$patch did not apply"
 	elif [[ "$output" =~ $drift_regex ]]; then
-		echo "$output" >&2
+		[[ -v VERBOSE ]] && echo "$output" >&2
 		warn "${patch} applied with fuzz"
 	fi
 
@@ -544,7 +543,11 @@ build_kernel() {
 	#
 	cmd+=("KBUILD_MODPOST_WARN=1")
 
-	cmd+=("$VERBOSE")
+	if [[ -v VERBOSE ]]; then
+		cmd+=("V=1")
+	else
+		cmd+=("-s")
+	fi
 	cmd+=("-j$JOBS")
 	cmd+=("KCFLAGS=-ffunction-sections -fdata-sections")
 	cmd+=("OBJTOOL_ARGS=${objtool_args[*]}")
@@ -805,7 +808,11 @@ build_patch_module() {
 	[[ $REPLACE -eq 0 ]] && cflags+=("-DKLP_NO_REPLACE")
 
 	cmd=("make")
-	cmd+=("$VERBOSE")
+	if [[ -v VERBOSE ]]; then
+		cmd+=("V=1")
+	else
+		cmd+=("-s")
+	fi
 	cmd+=("-j$JOBS")
 	cmd+=("--directory=.")
 	cmd+=("M=$KMOD_DIR")
-- 
2.53.0

[PATCH v2 28/53] klp-build: Fix patch cleanup on interrupt

[Josh Poimboeuf]

If a build error occurs and the user hits Ctrl-C while a large patch is
being reverted during cleanup, the cleanup EXIT trap gets re-triggered
and tries to re-revert the already partially-reverted patch.  That
causes 'patch -R' to repeatedly prompt

  "Unreversed patch detected!  Ignore -R? [n]"

for each already-reverted hunk, with no way to break out.

Fix it by adding '--force' to the patch revert command in
revert_patch(), which causes it to silently ignore already-reverted
hunks.  And ignore errors, as the cleanup is always best-effort.

For similar reasons, add to APPLIED_PATCHES before (rather than after)
applying the patch in apply_patch() so an interrupted apply will also
get cleaned up.

Fixes: d36a7343f4ba ("livepatch/klp-build: switch to GNU patch and recountdiff")
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 scripts/livepatch/klp-build | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index dc2c5c33d1db..9970e1f274ef 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -384,15 +384,15 @@ apply_patch() {
 		warn "${patch} applied with fuzz"
 	fi
 
-	patch -d "$SRC" -p1 --no-backup-if-mismatch -r /dev/null "${extra_args[@]}" --silent < "$patch"
 	APPLIED_PATCHES+=("$patch")
+	patch -d "$SRC" -p1 --no-backup-if-mismatch -r /dev/null "${extra_args[@]}" --silent < "$patch"
 }
 
 revert_patch() {
 	local patch="$1"
 	local tmp=()
 
-	patch -d "$SRC" -p1 -R --silent --no-backup-if-mismatch -r /dev/null < "$patch"
+	patch -d "$SRC" -p1 -R --force --no-backup-if-mismatch -r /dev/null &> /dev/null < "$patch" || true
 
 	for p in "${APPLIED_PATCHES[@]}"; do
 		[[ "$p" == "$patch" ]] && continue
-- 
2.53.0

[PATCH v2 29/53] klp-build: Reject patches to vDSO

[Josh Poimboeuf]

vDSO code runs in userspace and can't be livepatched.  Such patches also
cause spurious "new function" errors due to generated files like
vdso*-image.c having unstable line numbers across builds.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 scripts/livepatch/klp-build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index 9970e1f274ef..a70d48d98453 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -357,7 +357,7 @@ check_unsupported_patches() {
 
 		for file in "${files[@]}"; do
 			case "$file" in
-				lib/*|*.S)
+				lib/*|*/vdso/*|*.S)
 					die "${patch}: unsupported patch to $file"
 					;;
 			esac
-- 
2.53.0

[PATCH v2 30/53] klp-build: Reject patches to realmode

[Josh Poimboeuf]

Realmode code is compiled as a separate 16-bit binary and embedded into
the kernel image via rmpiggy.S.  It can't be livepatched.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 scripts/livepatch/klp-build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index a70d48d98453..2bb35de5db75 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -357,7 +357,7 @@ check_unsupported_patches() {
 
 		for file in "${files[@]}"; do
 			case "$file" in
-				lib/*|*/vdso/*|*.S)
+				lib/*|*/vdso/*|*/realmode/rm/*|*.S)
 					die "${patch}: unsupported patch to $file"
 					;;
 			esac
-- 
2.53.0

[PATCH v2 31/53] klp-build: Print "objtool klp diff" command in verbose mode

[Josh Poimboeuf]

Print the full objtool command line when '--verbose' is given to help
with debugging.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 scripts/livepatch/klp-build | 1 +
 1 file changed, 1 insertion(+)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index 2bb35de5db75..355345aa94d2 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -681,6 +681,7 @@ diff_objects() {
 
 		(
 			cd "$ORIG_DIR"
+			[[ -v VERBOSE ]] && echo "${cmd[@]}"
 			"${cmd[@]}"							\
 				1> >(tee -a "$log")					\
 				2> >(tee -a "$log" | "${filter[@]}" >&2) ||		\
-- 
2.53.0

[PATCH v2 32/53] klp-build: Remove redundant SRC and OBJ variables

[Josh Poimboeuf]

SRC and OBJ are both set to $(pwd) and are always identical.  The script
already enforces that klp-build runs from the kernel root directory, and
builds are done in-place, making these variables unnecessary.

Suggested-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 scripts/livepatch/klp-build | 67 ++++++++++++++++---------------------
 1 file changed, 28 insertions(+), 39 deletions(-)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index 355345aa94d2..34a46bafdaec 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -33,11 +33,9 @@ SCRIPT="$(basename "$0")"
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 FIX_PATCH_LINES="$SCRIPT_DIR/fix-patch-lines"
 
-SRC="$(pwd)"
-OBJ="$(pwd)"
-
-CONFIG="$OBJ/.config"
-TMP_DIR="$OBJ/klp-tmp"
+OBJTOOL="$PWD/tools/objtool/objtool"
+CONFIG="$PWD/.config"
+TMP_DIR="$PWD/klp-tmp"
 
 ORIG_DIR="$TMP_DIR/orig"
 PATCHED_DIR="$TMP_DIR/patched"
@@ -88,7 +86,7 @@ declare -a STASHED_FILES
 
 stash_file() {
 	local file="$1"
-	local rel_file="${file#"$SRC"/}"
+	local rel_file="${file#"$PWD"/}"
 
 	[[ ! -e "$file" ]] && die "no file to stash: $file"
 
@@ -102,7 +100,7 @@ restore_files() {
 	local file
 
 	for file in "${STASHED_FILES[@]}"; do
-		mv -f "$STASH_DIR/$file" "$SRC/$file" || warn "can't restore file: $file"
+		mv -f "$STASH_DIR/$file" "$PWD/$file" || warn "can't restore file: $file"
 	done
 
 	STASHED_FILES=()
@@ -304,7 +302,7 @@ set_module_name() {
 # Hardcode the value printed by the localversion script to prevent patch
 # application from appending it with '+' due to a dirty working tree.
 set_kernelversion() {
-	local file="$SRC/scripts/setlocalversion"
+	local file="$PWD/scripts/setlocalversion"
 	local kernelrelease
 
 	stash_file "$file"
@@ -375,7 +373,7 @@ apply_patch() {
 
 	[[ ! -f "$patch" ]] && die "$patch doesn't exist"
 	status=0
-	output=$(patch -d "$SRC" -p1 --dry-run --no-backup-if-mismatch -r /dev/null "${extra_args[@]}" < "$patch" 2>&1) || status=$?
+	output=$(patch -p1 --dry-run --no-backup-if-mismatch -r /dev/null "${extra_args[@]}" < "$patch" 2>&1) || status=$?
 	if [[ "$status" -ne 0 ]]; then
 		echo "$output" >&2
 		die "$patch did not apply"
@@ -385,14 +383,14 @@ apply_patch() {
 	fi
 
 	APPLIED_PATCHES+=("$patch")
-	patch -d "$SRC" -p1 --no-backup-if-mismatch -r /dev/null "${extra_args[@]}" --silent < "$patch"
+	patch -p1 --no-backup-if-mismatch -r /dev/null "${extra_args[@]}" --silent < "$patch"
 }
 
 revert_patch() {
 	local patch="$1"
 	local tmp=()
 
-	patch -d "$SRC" -p1 -R --force --no-backup-if-mismatch -r /dev/null &> /dev/null < "$patch" || true
+	patch -p1 -R --force --no-backup-if-mismatch -r /dev/null &> /dev/null < "$patch" || true
 
 	for p in "${APPLIED_PATCHES[@]}"; do
 		[[ "$p" == "$patch" ]] && continue
@@ -430,8 +428,7 @@ validate_patches() {
 do_init() {
 	# We're not yet smart enough to handle anything other than in-tree
 	# builds in pwd.
-	[[ ! "$SRC" -ef "$SCRIPT_DIR/../.." ]] && die "please run from the kernel root directory"
-	[[ ! "$OBJ" -ef "$SCRIPT_DIR/../.." ]] && die "please run from the kernel root directory"
+	[[ ! "$PWD" -ef "$SCRIPT_DIR/../.." ]] && die "please run from the kernel root directory"
 
 	(( SHORT_CIRCUIT <= 1 )) && rm -rf "$TMP_DIR"
 	mkdir -p "$TMP_DIR"
@@ -462,11 +459,11 @@ refresh_patch() {
 	get_patch_output_files "$patch" | mapfile -t output_files
 
 	# Copy orig source files to 'a'
-	( cd "$SRC" && echo "${input_files[@]}" | xargs cp --parents --target-directory="$tmpdir/a" )
+	echo "${input_files[@]}" | xargs cp --parents --target-directory="$tmpdir/a"
 
 	# Copy patched source files to 'b'
 	apply_patch "$patch" "--silent"
-	( cd "$SRC" && echo "${output_files[@]}" | xargs cp --parents --target-directory="$tmpdir/b" )
+	echo "${output_files[@]}" | xargs cp --parents --target-directory="$tmpdir/b"
 	revert_patch "$patch"
 
 	# Diff 'a' and 'b' to make a clean patch
@@ -510,10 +507,7 @@ clean_kernel() {
 	cmd+=("-j$JOBS")
 	cmd+=("clean")
 
-	(
-		cd "$SRC"
-		"${cmd[@]}"
-	)
+	"${cmd[@]}"
 }
 
 build_kernel() {
@@ -554,12 +548,10 @@ build_kernel() {
 	cmd+=("vmlinux")
 	cmd+=("modules")
 
-	(
-		cd "$SRC"
-		"${cmd[@]}"							\
-			1> >(tee -a "$log")					\
-			2> >(tee -a "$log" | grep0 -v "modpost.*undefined!" >&2)
-	) || die "$build kernel build failed"
+	"${cmd[@]}"							\
+		1> >(tee -a "$log")					\
+		2> >(tee -a "$log" | grep0 -v "modpost.*undefined!" >&2) \
+		|| die "$build kernel build failed"
 }
 
 find_objects() {
@@ -567,9 +559,9 @@ find_objects() {
 
 	# Find root-level vmlinux.o and non-root-level .ko files,
 	# excluding klp-tmp/ and .git/
-	find "$OBJ" \( -path "$TMP_DIR" -o -path "$OBJ/.git" -o	-regex "$OBJ/[^/][^/]*\.ko" \) -prune -o \
+	find "$PWD" \( -path "$TMP_DIR" -o -path "$PWD/.git" -o -regex "$PWD/[^/][^/]*\.ko" \) -prune -o \
 		    -type f "${opts[@]}"				\
-		    \( -name "*.ko" -o -path "$OBJ/vmlinux.o" \)	\
+		    \( -name "*.ko" -o -path "$PWD/vmlinux.o" \)	\
 		    -printf '%P\n'
 }
 
@@ -585,7 +577,7 @@ copy_orig_objects() {
 	xtrace_save "copying orig objects"
 	for _file in "${files[@]}"; do
 		local rel_file="${_file/.ko/.o}"
-		local file="$OBJ/$rel_file"
+		local file="$PWD/$rel_file"
 		local orig_file="$ORIG_DIR/$rel_file"
 		local orig_dir="$(dirname "$orig_file")"
 
@@ -618,7 +610,7 @@ copy_patched_objects() {
 	xtrace_save "copying changed objects"
 	for _file in "${files[@]}"; do
 		local rel_file="${_file/.ko/.o}"
-		local file="$OBJ/$rel_file"
+		local file="$PWD/$rel_file"
 		local orig_file="$ORIG_DIR/$rel_file"
 		local patched_file="$PATCHED_DIR/$rel_file"
 		local patched_dir="$(dirname "$patched_file")"
@@ -663,7 +655,7 @@ diff_objects() {
 
 		mkdir -p "$(dirname "$out_file")"
 
-		cmd=("$SRC/tools/objtool/objtool")
+		cmd=("$OBJTOOL")
 		cmd+=("klp")
 		cmd+=("diff")
 		(( ${#opts[@]} > 0 )) && cmd+=("${opts[@]}")
@@ -716,7 +708,7 @@ diff_checksums() {
 		fi
 	done
 
-	cmd=("$SRC/tools/objtool/objtool")
+	cmd=("$OBJTOOL")
 	cmd+=("--checksum")
 	cmd+=("--link")
 	cmd+=("--dry-run")
@@ -774,7 +766,7 @@ build_patch_module() {
 	rm -rf "$KMOD_DIR"
 	mkdir -p "$KMOD_DIR"
 
-	cp -f "$SRC/scripts/livepatch/init.c" "$KMOD_DIR"
+	cp -f "$SCRIPT_DIR/init.c" "$KMOD_DIR"
 
 	echo "obj-m := $NAME.o" > "$makefile"
 	echo -n "$NAME-y := init.o" >> "$makefile"
@@ -820,12 +812,9 @@ build_patch_module() {
 	cmd+=("KCFLAGS=${cflags[*]}")
 
 	# Build a "normal" kernel module with init.c and the diffed objects
-	(
-		cd "$SRC"
-		"${cmd[@]}"							\
-			1> >(tee -a "$log")					\
-			2> >(tee -a "$log" >&2)
-	)
+	"${cmd[@]}"							\
+		1> >(tee -a "$log")					\
+		2> >(tee -a "$log" >&2)
 
 	kmod_file="$KMOD_DIR/$NAME.ko"
 
@@ -836,7 +825,7 @@ build_patch_module() {
 	objcopy --remove-section=.BTF "$kmod_file"
 
 	# Fix (and work around) linker wreckage for klp syms / relocs
-	"$SRC/tools/objtool/objtool" klp post-link "$kmod_file" || die "objtool klp post-link failed"
+	"$OBJTOOL" klp post-link "$kmod_file" || die "objtool klp post-link failed"
 
 	cp -f "$kmod_file" "$OUTFILE"
 }
-- 
2.53.0

Re: [PATCH v2 32/53] klp-build: Remove redundant SRC and OBJ variables

[Song Liu]

On Fri, May 1, 2026 at 5:09 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> SRC and OBJ are both set to $(pwd) and are always identical.  The script
> already enforces that klp-build runs from the kernel root directory, and
> builds are done in-place, making these variables unnecessary.
>
> Suggested-by: Song Liu <song@kernel.org>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

[PATCH v2 33/53] objtool/klp: Don't set sym->file for section symbols

[Josh Poimboeuf]

Section symbols aren't grouped after their corresponding FILE symbols.
Their sym->file should really be NULL rather than whatever random FILE
happened to be last.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/elf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index f41280e454ca..d9cee8d5d9e8 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -649,7 +649,7 @@ static int read_symbols(struct elf *elf)
 
 		if (is_file_sym(sym))
 			file = sym;
-		else if (sym->bind == STB_LOCAL)
+		else if (sym->bind == STB_LOCAL && !is_sec_sym(sym))
 			sym->file = file;
 	}
 
-- 
2.53.0

[PATCH v2 34/53] objtool: Include libsubcmd headers directly from source tree

[Josh Poimboeuf]

Instead of installing libsubcmd headers to a build output directory and
including from there, include directly from tools/lib/ where they
already exist.  This fixes clangd indexing which otherwise can't find
libsubcmd headers.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/Makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
index b71d1886022e..a4484fd22a96 100644
--- a/tools/objtool/Makefile
+++ b/tools/objtool/Makefile
@@ -58,7 +58,7 @@ INCLUDES := -I$(srctree)/tools/include \
 	    -I$(srctree)/tools/arch/$(SRCARCH)/include	\
 	    -I$(srctree)/tools/objtool/include \
 	    -I$(srctree)/tools/objtool/arch/$(SRCARCH)/include \
-	    -I$(LIBSUBCMD_OUTPUT)/include
+	    -I$(srctree)/tools/lib
 
 OBJTOOL_CFLAGS  := -std=gnu11 -fomit-frame-pointer -O2 -g $(WARNINGS)	\
 		   $(INCLUDES) $(LIBELF_FLAGS) $(LIBXXHASH_CFLAGS) $(HOSTCFLAGS)
@@ -135,7 +135,7 @@ $(LIBSUBCMD): fixdep $(LIBSUBCMD_OUTPUT) FORCE
 	$(Q)$(MAKE) -C $(LIBSUBCMD_DIR) O=$(LIBSUBCMD_OUTPUT) \
 		DESTDIR=$(LIBSUBCMD_OUTPUT) prefix= subdir= \
 		$(HOST_OVERRIDES) EXTRA_CFLAGS="$(OBJTOOL_CFLAGS)" \
-		$@ install_headers
+		$@
 
 $(LIBSUBCMD)-clean:
 	$(call QUIET_CLEAN, libsubcmd)
-- 
2.53.0

[PATCH v2 35/53] objtool/klp: Create empty checksum sections for function-less object files

[Josh Poimboeuf]

If an object file has no functions, objtool has nothing to checksum, so
it doesn't create the .discard.sym_checksum symbol.

Then when 'objtool klp diff' reads symbol checksums, it errors out due
to the missing .discard.sym_checksum section.

Instead, just create an empty checksum section to signal to
read_sym_checksums() that the file has been processed.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/check.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index e7579c4e46dc..f020f21f94a7 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1044,9 +1044,6 @@ static int create_sym_checksum_section(struct objtool_file *file)
 		if (sym->csum.checksum)
 			idx++;
 
-	if (!idx)
-		return 0;
-
 	sec = elf_create_section_pair(file->elf, ".discard.sym_checksum", entsize,
 				      idx, idx);
 	if (!sec)
-- 
2.53.0

[PATCH v2 36/53] objtool/klp: Handle Clang .data..Lanon anonymous data sections

[Josh Poimboeuf]

Clang generates anonymous data sections named .data..Lanon.<hash>.
These need section-symbol references in the same way as .data..Lubsan
(GCC) and .data..L__unnamed_ (Clang UBSAN) sections.  Without this,
convert_reloc_sym() fails when processing relocations that reference
these sections.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 463b6daa5234..7e58ef36f805 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -1030,14 +1030,15 @@ static int convert_reloc_secsym_to_sym(struct elf *elf, struct reloc *reloc)
 }
 
 /*
- * Sections with anonymous or uncorrelated data (strings, UBSAN data)
- * need section symbol references.
+ * Sections with anonymous or uncorrelated data (strings, UBSAN data, Clang
+ * anonymous constants) need section symbol references.
  */
 static bool is_uncorrelated_section(struct section *sec)
 {
 	return is_string_sec(sec) ||
 	       strstarts(sec->name, ".data..Lubsan") ||		/* GCC */
-	       strstarts(sec->name, ".data..L__unnamed_");	/* Clang */
+	       strstarts(sec->name, ".data..L__unnamed_") ||	/* Clang */
+	       strstarts(sec->name, ".data..Lanon.");		/* Clang */
 }
 
 /*
-- 
2.53.0

[PATCH v2 37/53] objtool: Add is_alias_sym() helper

[Josh Poimboeuf]

Improve readability with a new is_alias_sym() helper.

No functional changes intended.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/check.c               | 6 +++---
 tools/objtool/include/objtool/elf.h | 5 +++++
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index f020f21f94a7..6c94eb32c090 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -491,7 +491,7 @@ static int decode_instructions(struct objtool_file *file)
 				return -1;
 			}
 
-			if (func->embedded_insn || func->alias != func)
+			if (func->embedded_insn || is_alias_sym(func))
 				continue;
 
 			if (!find_insn(file, sec, func->offset)) {
@@ -2229,7 +2229,7 @@ static int add_jump_table_alts(struct objtool_file *file)
 		return 0;
 
 	for_each_sym(file->elf, func) {
-		if (!is_func_sym(func) || func->alias != func)
+		if (!is_func_sym(func) || is_alias_sym(func))
 			continue;
 
 		mark_func_jump_tables(file, func);
@@ -4523,7 +4523,7 @@ static int validate_symbol(struct objtool_file *file, struct section *sec,
 		return 1;
 	}
 
-	if (sym->pfunc != sym || sym->alias != sym)
+	if (sym->pfunc != sym || is_alias_sym(sym))
 		return 0;
 
 	insn = find_insn(file, sec, sym->offset);
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index 8a543cea43b9..ccc72a692d9a 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -298,6 +298,11 @@ static inline bool is_local_sym(struct symbol *sym)
 	return sym->bind == STB_LOCAL;
 }
 
+static inline bool is_alias_sym(struct symbol *sym)
+{
+	return sym->alias != sym;
+}
+
 static inline bool is_prefix_func(struct symbol *sym)
 {
 	return sym->prefix;
-- 
2.53.0

[PATCH v2 38/53] objtool: Add is_cold_func() helper

[Josh Poimboeuf]

Add an is_cold_func() helper.  No functional changes intended.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/check.c               | 6 +++---
 tools/objtool/include/objtool/elf.h | 5 +++++
 tools/objtool/klp-diff.c            | 3 ++-
 3 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 6c94eb32c090..93a054adf209 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2614,7 +2614,7 @@ static void mark_holes(struct objtool_file *file)
 		if (insn->jump_dest) {
 			struct symbol *dest_func = insn_func(insn->jump_dest);
 
-			if (dest_func && dest_func->cold)
+			if (dest_func && is_cold_func(dest_func))
 				dest_func->ignore = true;
 		}
 	}
@@ -4422,8 +4422,8 @@ static int create_prefix_symbol(struct objtool_file *file, struct symbol *func)
 	char name[SYM_NAME_LEN];
 	struct cfi_state *cfi;
 
-	if (!is_func_sym(func) || is_prefix_func(func) ||
-	    func->cold || func->static_call_tramp)
+	if (!is_func_sym(func) || is_prefix_func(func) || is_cold_func(func) ||
+	    func->static_call_tramp)
 		return 0;
 
 	if ((strlen(func->name) + sizeof("__pfx_") > SYM_NAME_LEN)) {
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index ccc72a692d9a..e452784df702 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -308,6 +308,11 @@ static inline bool is_prefix_func(struct symbol *sym)
 	return sym->prefix;
 }
 
+static inline bool is_cold_func(struct symbol *sym)
+{
+	return sym->cold;
+}
+
 static inline bool is_reloc_sec(struct section *sec)
 {
 	return sec->sh.sh_type == SHT_RELA || sec->sh.sh_type == SHT_REL;
diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 7e58ef36f805..8728dda1e08c 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -1709,7 +1709,8 @@ static int create_klp_sections(struct elfs *e)
 		unsigned long sympos;
 		void *func_data;
 
-		if (!is_func_sym(sym) || sym->cold || !sym->clone || !sym->clone->changed)
+		if (!is_func_sym(sym) || is_cold_func(sym) ||
+		    !sym->clone || !sym->clone->changed)
 			continue;
 
 		/* allocate klp_func_ext */
-- 
2.53.0

Re: [PATCH v2 38/53] objtool: Add is_cold_func() helper

[Song Liu]

On Fri, May 1, 2026 at 5:11 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> Add an is_cold_func() helper.  No functional changes intended.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

[PATCH v2 39/53] objtool/klp: Extricate checksum calculation from validate_branch()

[Josh Poimboeuf]

In preparation for porting the checksum code to other arches, make its
functionality independent from the CFG reverse engineering code.

Move it into a standalone calculate_checksums() function which iterates
all functions and instructions directly, rather than being called inline
from do_validate_branch().

Since checksum_update_insn() is no longer called during CFG traversal,
it needs to manually iterate the alternatives.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/check.c                    | 106 +++++++++++++++++------
 tools/objtool/include/objtool/checksum.h |   6 +-
 2 files changed, 80 insertions(+), 32 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 93a054adf209..f019e1f06780 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1350,10 +1350,7 @@ static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *i
 {
 	struct reloc *reloc;
 
-	if (insn->no_reloc)
-		return NULL;
-
-	if (!file)
+	if (!file || insn->no_reloc || insn->fake)
 		return NULL;
 
 	reloc = find_reloc_by_dest_range(file->elf, insn->sec,
@@ -2622,9 +2619,17 @@ static void mark_holes(struct objtool_file *file)
 
 static bool validate_branch_enabled(void)
 {
-	return opts.stackval ||
-	       opts.orc ||
-	       opts.uaccess ||
+	return opts.stackval	||
+	       opts.orc		||
+	       opts.uaccess;
+}
+
+static bool alts_needed(void)
+{
+	return validate_branch_enabled()	||
+	       opts.noinstr			||
+	       opts.hack_jump_label		||
+	       opts.disas			||
 	       opts.checksum;
 }
 
@@ -2658,7 +2663,7 @@ static int decode_sections(struct objtool_file *file)
 	 * Must be before add_jump_destinations(), which depends on 'func'
 	 * being set for alternatives, to enable proper sibling call detection.
 	 */
-	if (validate_branch_enabled() || opts.noinstr || opts.hack_jump_label || opts.disas) {
+	if (alts_needed()) {
 		if (add_special_section_alts(file))
 			return -1;
 	}
@@ -3654,6 +3659,7 @@ static bool skip_alt_group(struct instruction *insn)
 	return alt_insn->type == INSN_CLAC || alt_insn->type == INSN_STAC;
 }
 
+#ifdef BUILD_KLP
 static int checksum_debug_init(struct objtool_file *file)
 {
 	char *dup, *s;
@@ -3701,8 +3707,10 @@ static void checksum_update_insn(struct objtool_file *file, struct symbol *func,
 				 struct instruction *insn)
 {
 	struct reloc *reloc = insn_reloc(file, insn);
+	struct alternative *alt;
 	unsigned long offset;
 	struct symbol *sym;
+	static bool in_alt;
 
 	if (insn->fake)
 		return;
@@ -3715,7 +3723,7 @@ static void checksum_update_insn(struct objtool_file *file, struct symbol *func,
 		if (call_dest)
 			checksum_update(func, insn, call_dest->demangled_name,
 					strlen(call_dest->demangled_name));
-		return;
+		goto alts;
 	}
 
 	sym = reloc->sym;
@@ -3726,21 +3734,78 @@ static void checksum_update_insn(struct objtool_file *file, struct symbol *func,
 
 		str = sym->sec->data->d_buf + sym->offset + offset;
 		checksum_update(func, insn, str, strlen(str));
-		return;
+		goto alts;
 	}
 
 	if (is_sec_sym(sym)) {
 		sym = find_symbol_containing(reloc->sym->sec, offset);
 		if (!sym)
-			return;
+			goto alts;
 
 		offset -= sym->offset;
 	}
 
 	checksum_update(func, insn, sym->demangled_name, strlen(sym->demangled_name));
 	checksum_update(func, insn, &offset, sizeof(offset));
+
+alts:
+	for (alt = insn->alts; alt; alt = alt->next) {
+		struct alt_group *alt_group = alt->insn->alt_group;
+
+		/* Prevent __ex_table recursion, e.g. LOAD_SEGMENT() */
+		if (in_alt)
+			break;
+		in_alt = true;
+
+		checksum_update(func, insn, &alt->type, sizeof(alt->type));
+
+		if (alt_group && alt_group->orig_group) {
+			struct instruction *alt_insn;
+
+			checksum_update(func, insn, &alt_group->feature, sizeof(alt_group->feature));
+
+			for (alt_insn = alt->insn; alt_insn; alt_insn = next_insn_same_sec(file, alt_insn)) {
+				checksum_update_insn(file, func, alt_insn);
+				if (!alt_group->last_insn || alt_insn == alt_group->last_insn)
+					break;
+			}
+		} else {
+			checksum_update_insn(file, func, alt->insn);
+		}
+
+		in_alt = false;
+	}
 }
 
+static int calculate_checksums(struct objtool_file *file)
+{
+	struct instruction *insn;
+	struct symbol *func;
+
+	if (checksum_debug_init(file))
+		return -1;
+
+	for_each_sym(file->elf, func) {
+		/*
+		 * Skip cold subfunctions and aliases: they share the
+		 * parent's checksum via func_for_each_insn() which
+		 * follows func->cfunc into the cold subfunction.
+		 */
+		if (!is_func_sym(func) || is_cold_func(func) ||
+		    is_alias_sym(func) || !func->len)
+			continue;
+
+		checksum_init(func);
+
+		func_for_each_insn(file, func, insn)
+			checksum_update_insn(file, func, insn);
+
+		checksum_finish(func);
+	}
+	return 0;
+}
+#endif /* BUILD_KLP */
+
 static int validate_branch(struct objtool_file *file, struct symbol *func,
 			   struct instruction *insn, struct insn_state state);
 static int do_validate_branch(struct objtool_file *file, struct symbol *func,
@@ -4022,9 +4087,6 @@ static int do_validate_branch(struct objtool_file *file, struct symbol *func,
 		insn->trace = 0;
 		next_insn = next_insn_to_validate(file, insn);
 
-		if (opts.checksum && func && insn->sec)
-			checksum_update_insn(file, func, insn);
-
 		if (func && insn_func(insn) && func != insn_func(insn)->pfunc) {
 			/* Ignore KCFI type preambles, which always fall through */
 			if (is_prefix_func(func))
@@ -4090,9 +4152,6 @@ static int validate_unwind_hint(struct objtool_file *file,
 		struct symbol *func = insn_func(insn);
 		int ret;
 
-		if (opts.checksum)
-			checksum_init(func);
-
 		ret = validate_branch(file, func, insn, *state);
 		if (ret)
 			BT_INSN(insn, "<=== (hint)");
@@ -4535,9 +4594,6 @@ static int validate_symbol(struct objtool_file *file, struct section *sec,
 
 	func = insn_func(insn);
 
-	if (opts.checksum)
-		checksum_init(func);
-
 	if (opts.trace && !fnmatch(opts.trace, sym->name, 0)) {
 		trace_enable();
 		TRACE("%s: validation begin\n", sym->name);
@@ -4550,9 +4606,6 @@ static int validate_symbol(struct objtool_file *file, struct section *sec,
 	TRACE("%s: validation %s\n\n", sym->name, ret ? "failed" : "end");
 	trace_disable();
 
-	if (opts.checksum)
-		checksum_finish(func);
-
 	return ret;
 }
 
@@ -5007,10 +5060,6 @@ int check(struct objtool_file *file)
 	cfi_hash_add(&init_cfi);
 	cfi_hash_add(&func_cfi);
 
-	ret = checksum_debug_init(file);
-	if (ret)
-		goto out;
-
 	ret = decode_sections(file);
 	if (ret)
 		goto out;
@@ -5101,6 +5150,9 @@ int check(struct objtool_file *file)
 		warnings += check_abs_references(file);
 
 	if (opts.checksum) {
+		ret = calculate_checksums(file);
+		if (ret)
+			goto out;
 		ret = create_sym_checksum_section(file);
 		if (ret)
 			goto out;
diff --git a/tools/objtool/include/objtool/checksum.h b/tools/objtool/include/objtool/checksum.h
index 0bd16fe9168b..3f25df90305d 100644
--- a/tools/objtool/include/objtool/checksum.h
+++ b/tools/objtool/include/objtool/checksum.h
@@ -33,11 +33,7 @@ static inline void checksum_finish(struct symbol *func)
 
 #else /* !BUILD_KLP */
 
-static inline void checksum_init(struct symbol *func) {}
-static inline void checksum_update(struct symbol *func,
-				   struct instruction *insn,
-				   const void *data, size_t size) {}
-static inline void checksum_finish(struct symbol *func) {}
+static inline int calculate_checksums(struct objtool_file *file) { return -ENOSYS; }
 
 #endif /* !BUILD_KLP */
 
-- 
2.53.0

[PATCH v2 40/53] objtool: Consolidate file decoding into decode_file()

[Josh Poimboeuf]

decode_sections() relies on CFI and cfi_hash initialization done
separately in check(), making it unusable outside of check().

Consolidate the initialization into decode_sections() and rename it to
decode_file(), and make it global along with free_insns() and
insn_reloc() for use by other objtool components -- namely, the checksum
code which will be moving to another file.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/check.c                 | 36 +++++++++++++--------------
 tools/objtool/include/objtool/check.h |  5 ++++
 2 files changed, 22 insertions(+), 19 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index f019e1f06780..49171ddc6f54 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1346,7 +1346,7 @@ __weak bool arch_is_embedded_insn(struct symbol *sym)
 	return false;
 }
 
-static struct reloc *insn_reloc(struct objtool_file *file, struct instruction *insn)
+struct reloc *insn_reloc(struct objtool_file *file, struct instruction *insn)
 {
 	struct reloc *reloc;
 
@@ -2633,8 +2633,21 @@ static bool alts_needed(void)
 	       opts.checksum;
 }
 
-static int decode_sections(struct objtool_file *file)
+int decode_file(struct objtool_file *file)
 {
+	arch_initial_func_cfi_state(&initial_func_cfi);
+	init_cfi_state(&init_cfi);
+	init_cfi_state(&func_cfi);
+	set_func_state(&func_cfi);
+	init_cfi_state(&force_undefined_cfi);
+	force_undefined_cfi.force_undefined = true;
+
+	if (!cfi_hash_alloc(1UL << (file->elf->symbol_bits - 3)))
+		return -1;
+
+	cfi_hash_add(&init_cfi);
+	cfi_hash_add(&func_cfi);
+
 	file->klp = is_livepatch_module(file);
 
 	mark_rodata(file);
@@ -4998,7 +5011,7 @@ struct insn_chunk {
  * which can trigger more allocations for .debug_* sections whose data hasn't
  * been read yet.
  */
-static void free_insns(struct objtool_file *file)
+void free_insns(struct objtool_file *file)
 {
 	struct instruction *insn;
 	struct insn_chunk *chunks = NULL, *chunk;
@@ -5045,22 +5058,7 @@ int check(struct objtool_file *file)
 		objtool_disas_ctx = disas_ctx;
 	}
 
-	arch_initial_func_cfi_state(&initial_func_cfi);
-	init_cfi_state(&init_cfi);
-	init_cfi_state(&func_cfi);
-	set_func_state(&func_cfi);
-	init_cfi_state(&force_undefined_cfi);
-	force_undefined_cfi.force_undefined = true;
-
-	if (!cfi_hash_alloc(1UL << (file->elf->symbol_bits - 3))) {
-		ret = -1;
-		goto out;
-	}
-
-	cfi_hash_add(&init_cfi);
-	cfi_hash_add(&func_cfi);
-
-	ret = decode_sections(file);
+	ret = decode_file(file);
 	if (ret)
 		goto out;
 
diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h
index 5f2f77bd9b41..6489e52ea2f2 100644
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@@ -155,6 +155,11 @@ struct instruction *next_insn_same_sec(struct objtool_file *file, struct instruc
 	     insn && insn->offset < sym->offset + sym->len;		\
 	     insn = next_insn_same_sec(file, insn))
 
+struct reloc *insn_reloc(struct objtool_file *file, struct instruction *insn);
+
+int decode_file(struct objtool_file *file);
+void free_insns(struct objtool_file *file);
+
 const char *objtool_disas_insn(struct instruction *insn);
 
 extern size_t sym_name_max_len;
-- 
2.53.0

[PATCH v2 41/53] objtool/klp: Add "objtool klp checksum" subcommand

[Josh Poimboeuf]

Move the checksum functionality out of the main objtool command into a
new "objtool klp checksum" subcommand.

This has the benefit of making the code (and the patch generation
process itself) more modular.

For bisectability, both "objtool --checksum" and "objtool klp checksum"
work for now.  The former will be removed after klp-build has been
converted to use the new subcommand.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/Build                      |   2 +-
 tools/objtool/builtin-klp.c              |   1 +
 tools/objtool/check.c                    | 205 +-----------------
 tools/objtool/include/objtool/check.h    |   6 +
 tools/objtool/include/objtool/checksum.h |   4 +
 tools/objtool/include/objtool/klp.h      |   1 +
 tools/objtool/klp-checksum.c             | 253 +++++++++++++++++++++++
 tools/objtool/klp-diff.c                 |   2 +-
 8 files changed, 269 insertions(+), 205 deletions(-)
 create mode 100644 tools/objtool/klp-checksum.c

diff --git a/tools/objtool/Build b/tools/objtool/Build
index 600da051af12..93a37b0dfd31 100644
--- a/tools/objtool/Build
+++ b/tools/objtool/Build
@@ -12,7 +12,7 @@ objtool-$(BUILD_DISAS) += disas.o
 objtool-$(BUILD_DISAS) += trace.o
 
 objtool-$(BUILD_ORC) += orc_gen.o orc_dump.o
-objtool-$(BUILD_KLP) += builtin-klp.o klp-diff.o klp-post-link.o
+objtool-$(BUILD_KLP) += builtin-klp.o klp-checksum.o klp-diff.o klp-post-link.o
 
 objtool-y += libstring.o
 objtool-y += libctype.o
diff --git a/tools/objtool/builtin-klp.c b/tools/objtool/builtin-klp.c
index 56d5a5b92f72..58c3b9bda3eb 100644
--- a/tools/objtool/builtin-klp.c
+++ b/tools/objtool/builtin-klp.c
@@ -13,6 +13,7 @@ struct subcmd {
 };
 
 static struct subcmd subcmds[] = {
+	{ "checksum",		"Generate per-function checksums",			cmd_klp_checksum, },
 	{ "diff",		"Generate binary diff of two object files",		cmd_klp_diff, },
 	{ "post-link",		"Finalize klp symbols/relocs after module linking",	cmd_klp_post_link, },
 };
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 49171ddc6f54..3e5d335d0e29 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -64,8 +64,8 @@ struct instruction *next_insn_same_sec(struct objtool_file *file,
 	return insn;
 }
 
-static struct instruction *next_insn_same_func(struct objtool_file *file,
-					       struct instruction *insn)
+struct instruction *next_insn_same_func(struct objtool_file *file,
+				       struct instruction *insn)
 {
 	struct instruction *next = next_insn_same_sec(file, insn);
 	struct symbol *func = insn_func(insn);
@@ -113,10 +113,6 @@ static struct instruction *prev_insn_same_sym(struct objtool_file *file,
 		for_each_sec(file->elf, __sec)				\
 			sec_for_each_insn(file, __sec, insn)
 
-#define func_for_each_insn(file, func, insn)				\
-	for (insn = find_insn(file, func->sec, func->offset);		\
-	     insn;							\
-	     insn = next_insn_same_func(file, insn))
 
 #define sym_for_each_insn(file, sym, insn)				\
 	for (insn = find_insn(file, sym->sec, sym->offset);		\
@@ -1023,56 +1019,6 @@ static int create_direct_call_sections(struct objtool_file *file)
 	return 0;
 }
 
-#ifdef BUILD_KLP
-static int create_sym_checksum_section(struct objtool_file *file)
-{
-	struct section *sec;
-	struct symbol *sym;
-	unsigned int idx = 0;
-	struct sym_checksum *checksum;
-	size_t entsize = sizeof(struct sym_checksum);
-
-	sec = find_section_by_name(file->elf, ".discard.sym_checksum");
-	if (sec) {
-		if (!opts.dryrun)
-			WARN("file already has .discard.sym_checksum section, skipping");
-
-		return 0;
-	}
-
-	for_each_sym(file->elf, sym)
-		if (sym->csum.checksum)
-			idx++;
-
-	sec = elf_create_section_pair(file->elf, ".discard.sym_checksum", entsize,
-				      idx, idx);
-	if (!sec)
-		return -1;
-
-	idx = 0;
-	for_each_sym(file->elf, sym) {
-		if (!sym->csum.checksum)
-			continue;
-
-		if (!elf_init_reloc(file->elf, sec->rsec, idx, idx * entsize,
-				    sym, 0, R_TEXT64))
-			return -1;
-
-		checksum = (struct sym_checksum *)sec->data->d_buf + idx;
-		checksum->addr = 0; /* reloc */
-		checksum->checksum = sym->csum.checksum;
-
-		mark_sec_changed(file->elf, sec, true);
-
-		idx++;
-	}
-
-	return 0;
-}
-#else
-static int create_sym_checksum_section(struct objtool_file *file) { return -EINVAL; }
-#endif
-
 /*
  * Warnings shouldn't be reported for ignored functions.
  */
@@ -3672,153 +3618,6 @@ static bool skip_alt_group(struct instruction *insn)
 	return alt_insn->type == INSN_CLAC || alt_insn->type == INSN_STAC;
 }
 
-#ifdef BUILD_KLP
-static int checksum_debug_init(struct objtool_file *file)
-{
-	char *dup, *s;
-
-	if (!opts.debug_checksum)
-		return 0;
-
-	dup = strdup(opts.debug_checksum);
-	if (!dup) {
-		ERROR_GLIBC("strdup");
-		return -1;
-	}
-
-	s = dup;
-	while (*s) {
-		bool found = false;
-		struct symbol *sym;
-		char *comma;
-
-		comma = strchr(s, ',');
-		if (comma)
-			*comma = '\0';
-
-		for_each_sym_by_name(file->elf, s, sym) {
-			if (!is_func_sym(sym))
-				continue;
-			sym->debug_checksum = 1;
-			found = true;
-		}
-
-		if (!found)
-			WARN("--debug-checksum: can't find '%s'", s);
-
-		if (!comma)
-			break;
-
-		s = comma + 1;
-	}
-
-	free(dup);
-	return 0;
-}
-
-static void checksum_update_insn(struct objtool_file *file, struct symbol *func,
-				 struct instruction *insn)
-{
-	struct reloc *reloc = insn_reloc(file, insn);
-	struct alternative *alt;
-	unsigned long offset;
-	struct symbol *sym;
-	static bool in_alt;
-
-	if (insn->fake)
-		return;
-
-	checksum_update(func, insn, insn->sec->data->d_buf + insn->offset, insn->len);
-
-	if (!reloc) {
-		struct symbol *call_dest = insn_call_dest(insn);
-
-		if (call_dest)
-			checksum_update(func, insn, call_dest->demangled_name,
-					strlen(call_dest->demangled_name));
-		goto alts;
-	}
-
-	sym = reloc->sym;
-	offset = arch_insn_adjusted_addend(insn, reloc);
-
-	if (is_string_sec(sym->sec)) {
-		char *str;
-
-		str = sym->sec->data->d_buf + sym->offset + offset;
-		checksum_update(func, insn, str, strlen(str));
-		goto alts;
-	}
-
-	if (is_sec_sym(sym)) {
-		sym = find_symbol_containing(reloc->sym->sec, offset);
-		if (!sym)
-			goto alts;
-
-		offset -= sym->offset;
-	}
-
-	checksum_update(func, insn, sym->demangled_name, strlen(sym->demangled_name));
-	checksum_update(func, insn, &offset, sizeof(offset));
-
-alts:
-	for (alt = insn->alts; alt; alt = alt->next) {
-		struct alt_group *alt_group = alt->insn->alt_group;
-
-		/* Prevent __ex_table recursion, e.g. LOAD_SEGMENT() */
-		if (in_alt)
-			break;
-		in_alt = true;
-
-		checksum_update(func, insn, &alt->type, sizeof(alt->type));
-
-		if (alt_group && alt_group->orig_group) {
-			struct instruction *alt_insn;
-
-			checksum_update(func, insn, &alt_group->feature, sizeof(alt_group->feature));
-
-			for (alt_insn = alt->insn; alt_insn; alt_insn = next_insn_same_sec(file, alt_insn)) {
-				checksum_update_insn(file, func, alt_insn);
-				if (!alt_group->last_insn || alt_insn == alt_group->last_insn)
-					break;
-			}
-		} else {
-			checksum_update_insn(file, func, alt->insn);
-		}
-
-		in_alt = false;
-	}
-}
-
-static int calculate_checksums(struct objtool_file *file)
-{
-	struct instruction *insn;
-	struct symbol *func;
-
-	if (checksum_debug_init(file))
-		return -1;
-
-	for_each_sym(file->elf, func) {
-		/*
-		 * Skip cold subfunctions and aliases: they share the
-		 * parent's checksum via func_for_each_insn() which
-		 * follows func->cfunc into the cold subfunction.
-		 */
-		if (!is_func_sym(func) || is_cold_func(func) ||
-		    is_alias_sym(func) || !func->len)
-			continue;
-
-		checksum_init(func);
-
-		func_for_each_insn(file, func, insn)
-			checksum_update_insn(file, func, insn);
-
-		checksum_finish(func);
-	}
-	return 0;
-}
-#endif /* BUILD_KLP */
-
 static int validate_branch(struct objtool_file *file, struct symbol *func,
 			   struct instruction *insn, struct insn_state state);
 static int do_validate_branch(struct objtool_file *file, struct symbol *func,
diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h
index 6489e52ea2f2..eea64728d39b 100644
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@@ -144,6 +144,12 @@ struct instruction *find_insn(struct objtool_file *file,
 			      struct section *sec, unsigned long offset);
 
 struct instruction *next_insn_same_sec(struct objtool_file *file, struct instruction *insn);
+struct instruction *next_insn_same_func(struct objtool_file *file, struct instruction *insn);
+
+#define func_for_each_insn(file, func, insn)				\
+	for (insn = find_insn(file, func->sec, func->offset);		\
+	     insn;							\
+	     insn = next_insn_same_func(file, insn))
 
 #define sec_for_each_insn(file, _sec, insn)				\
 	for (insn = find_insn(file, _sec, 0);				\
diff --git a/tools/objtool/include/objtool/checksum.h b/tools/objtool/include/objtool/checksum.h
index 3f25df90305d..be4eb7dfe6f2 100644
--- a/tools/objtool/include/objtool/checksum.h
+++ b/tools/objtool/include/objtool/checksum.h
@@ -31,9 +31,13 @@ static inline void checksum_finish(struct symbol *func)
 	}
 }
 
+int calculate_checksums(struct objtool_file *file);
+int create_sym_checksum_section(struct objtool_file *file);
+
 #else /* !BUILD_KLP */
 
 static inline int calculate_checksums(struct objtool_file *file) { return -ENOSYS; }
+static inline int create_sym_checksum_section(struct objtool_file *file) { return -EINVAL; }
 
 #endif /* !BUILD_KLP */
 
diff --git a/tools/objtool/include/objtool/klp.h b/tools/objtool/include/objtool/klp.h
index e32e5e8bc631..6f60cf05db86 100644
--- a/tools/objtool/include/objtool/klp.h
+++ b/tools/objtool/include/objtool/klp.h
@@ -29,6 +29,7 @@ struct klp_reloc {
 	u32 type;
 };
 
+int cmd_klp_checksum(int argc, const char **argv);
 int cmd_klp_diff(int argc, const char **argv);
 int cmd_klp_post_link(int argc, const char **argv);
 
diff --git a/tools/objtool/klp-checksum.c b/tools/objtool/klp-checksum.c
new file mode 100644
index 000000000000..e4a910f3211c
--- /dev/null
+++ b/tools/objtool/klp-checksum.c
@@ -0,0 +1,253 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <string.h>
+#include <subcmd/parse-options.h>
+
+#include <objtool/arch.h>
+#include <objtool/builtin.h>
+#include <objtool/check.h>
+#include <objtool/elf.h>
+#include <objtool/klp.h>
+#include <objtool/objtool.h>
+#include <objtool/warn.h>
+#include <objtool/checksum.h>
+
+static int checksum_debug_init(struct objtool_file *file)
+{
+	char *dup, *s;
+
+	if (!opts.debug_checksum)
+		return 0;
+
+	dup = strdup(opts.debug_checksum);
+	if (!dup) {
+		ERROR_GLIBC("strdup");
+		return -1;
+	}
+
+	s = dup;
+	while (*s) {
+		bool found = false;
+		struct symbol *sym;
+		char *comma;
+
+		comma = strchr(s, ',');
+		if (comma)
+			*comma = '\0';
+
+		for_each_sym_by_name(file->elf, s, sym) {
+			if (!is_func_sym(sym))
+				continue;
+			sym->debug_checksum = 1;
+			found = true;
+		}
+
+		if (!found)
+			WARN("--debug-checksum: can't find '%s'", s);
+
+		if (!comma)
+			break;
+
+		s = comma + 1;
+	}
+
+	free(dup);
+	return 0;
+}
+
+static void checksum_update_insn(struct objtool_file *file, struct symbol *func,
+				 struct instruction *insn)
+{
+	struct reloc *reloc = insn_reloc(file, insn);
+	struct alternative *alt;
+	unsigned long offset;
+	struct symbol *sym;
+	static bool in_alt;
+
+	if (insn->fake)
+		return;
+
+	checksum_update(func, insn, insn->sec->data->d_buf + insn->offset, insn->len);
+
+	if (!reloc) {
+		struct symbol *call_dest = insn_call_dest(insn);
+
+		if (call_dest)
+			checksum_update(func, insn, call_dest->demangled_name,
+					strlen(call_dest->demangled_name));
+		goto alts;
+	}
+
+	sym = reloc->sym;
+	offset = arch_insn_adjusted_addend(insn, reloc);
+
+	if (is_string_sec(sym->sec)) {
+		char *str;
+
+		str = sym->sec->data->d_buf + sym->offset + offset;
+		checksum_update(func, insn, str, strlen(str));
+		goto alts;
+	}
+
+	if (is_sec_sym(sym)) {
+		sym = find_symbol_containing(reloc->sym->sec, offset);
+		if (!sym)
+			goto alts;
+
+		offset -= sym->offset;
+	}
+
+	checksum_update(func, insn, sym->demangled_name, strlen(sym->demangled_name));
+	checksum_update(func, insn, &offset, sizeof(offset));
+
+alts:
+	for (alt = insn->alts; alt; alt = alt->next) {
+		struct alt_group *alt_group = alt->insn->alt_group;
+
+		/* Prevent __ex_table recursion, e.g. LOAD_SEGMENT() */
+		if (in_alt)
+			break;
+		in_alt = true;
+
+		checksum_update(func, insn, &alt->type, sizeof(alt->type));
+
+		if (alt_group && alt_group->orig_group) {
+			struct instruction *alt_insn;
+
+			checksum_update(func, insn, &alt_group->feature, sizeof(alt_group->feature));
+
+			for (alt_insn = alt->insn; alt_insn; alt_insn = next_insn_same_sec(file, alt_insn)) {
+				checksum_update_insn(file, func, alt_insn);
+				if (!alt_group->last_insn || alt_insn == alt_group->last_insn)
+					break;
+			}
+		} else {
+			checksum_update_insn(file, func, alt->insn);
+		}
+
+		in_alt = false;
+	}
+}
+
+int calculate_checksums(struct objtool_file *file)
+{
+	struct instruction *insn;
+	struct symbol *func;
+
+	if (checksum_debug_init(file))
+		return -1;
+
+	for_each_sym(file->elf, func) {
+		/*
+		 * Skip cold subfunctions and aliases: they share the
+		 * parent's checksum via func_for_each_insn() which
+		 * follows func->cfunc into the cold subfunction.
+		 */
+		if (!is_func_sym(func) || is_cold_func(func) ||
+		    is_alias_sym(func) || !func->len)
+			continue;
+
+		checksum_init(func);
+
+		func_for_each_insn(file, func, insn)
+			checksum_update_insn(file, func, insn);
+
+		checksum_finish(func);
+	}
+	return 0;
+}
+
+int create_sym_checksum_section(struct objtool_file *file)
+{
+	struct section *sec;
+	struct symbol *sym;
+	unsigned int idx = 0;
+	struct sym_checksum *checksum;
+	size_t entsize = sizeof(struct sym_checksum);
+
+	sec = find_section_by_name(file->elf, ".discard.sym_checksum");
+	if (sec) {
+		if (!opts.dryrun)
+			WARN("file already has .discard.sym_checksum section, skipping");
+
+		return 0;
+	}
+
+	for_each_sym(file->elf, sym)
+		if (sym->csum.checksum)
+			idx++;
+
+	sec = elf_create_section_pair(file->elf, ".discard.sym_checksum", entsize,
+				      idx, idx);
+	if (!sec)
+		return -1;
+
+	idx = 0;
+	for_each_sym(file->elf, sym) {
+		if (!sym->csum.checksum)
+			continue;
+
+		if (!elf_init_reloc(file->elf, sec->rsec, idx, idx * entsize,
+				    sym, 0, R_TEXT64))
+			return -1;
+
+		checksum = (struct sym_checksum *)sec->data->d_buf + idx;
+		checksum->addr = 0; /* reloc */
+		checksum->checksum = sym->csum.checksum;
+
+		mark_sec_changed(file->elf, sec, true);
+
+		idx++;
+	}
+
+	return 0;
+}
+
+static const char * const klp_checksum_usage[] = {
+	"objtool klp checksum [<options>] file.o",
+	NULL,
+};
+
+int cmd_klp_checksum(int argc, const char **argv)
+{
+	struct objtool_file *file;
+	int ret;
+
+	const struct option options[] = {
+		OPT_STRING(0,	"debug-checksum", &opts.debug_checksum,	"funcs", "enable checksum debug output"),
+		OPT_BOOLEAN(0,	"dry-run", &opts.dryrun, "don't write modifications"),
+		OPT_END(),
+	};
+
+	argc = parse_options(argc, argv, options, klp_checksum_usage, 0);
+	if (argc != 1)
+		usage_with_options(klp_checksum_usage, options);
+
+	opts.checksum = true;
+
+	objname = argv[0];
+
+	file = objtool_open_read(objname);
+	if (!file)
+		return 1;
+
+	ret = decode_file(file);
+	if (ret)
+		goto out;
+
+	ret = calculate_checksums(file);
+	if (ret)
+		goto out;
+
+	ret = create_sym_checksum_section(file);
+
+out:
+	free_insns(file);
+
+	if (ret)
+		return ret;
+
+	if (!opts.dryrun && file->elf->changed && elf_write(file->elf))
+		return 1;
+
+	return elf_close(file->elf);
+}
diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 8728dda1e08c..95359ad336bb 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -166,7 +166,7 @@ static int read_sym_checksums(struct elf *elf)
 
 	sec = find_section_by_name(elf, ".discard.sym_checksum");
 	if (!sec) {
-		ERROR("'%s' missing .discard.sym_checksum section, file not processed by 'objtool --checksum'?",
+		ERROR("'%s' missing .discard.sym_checksum section, file not processed by 'objtool klp checksum'?",
 		      elf->name);
 		return -1;
 	}
-- 
2.53.0

[PATCH v2 42/53] klp-build: Use "objtool klp checksum" subcommand

[Josh Poimboeuf]

Use the new "objtool klp checksum" subcommand instead of injecting
--checksum into every objtool invocation via OBJTOOL_ARGS during the
kernel build.

This decouples checksum generation from the build, running it in
separate post-build passes, making the code (and the patch generation
pipeline itself) more modular.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 scripts/livepatch/klp-build | 93 +++++++++++++++++++++++++------------
 1 file changed, 64 insertions(+), 29 deletions(-)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index 34a46bafdaec..8a4b268261a6 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -37,10 +37,12 @@ OBJTOOL="$PWD/tools/objtool/objtool"
 CONFIG="$PWD/.config"
 TMP_DIR="$PWD/klp-tmp"
 
-ORIG_DIR="$TMP_DIR/orig"
-PATCHED_DIR="$TMP_DIR/patched"
-DIFF_DIR="$TMP_DIR/diff"
-KMOD_DIR="$TMP_DIR/kmod"
+ORIG_DIR="$TMP_DIR/1-orig"
+PATCHED_DIR="$TMP_DIR/2-patched"
+ORIG_CSUM_DIR="$TMP_DIR/3-checksum-orig"
+PATCHED_CSUM_DIR="$TMP_DIR/3-checksum-patched"
+DIFF_DIR="$TMP_DIR/4-diff"
+KMOD_DIR="$TMP_DIR/5-kmod"
 
 STASH_DIR="$TMP_DIR/stash"
 TIMESTAMP="$TMP_DIR/timestamp"
@@ -136,10 +138,11 @@ Options:
 Advanced Options:
    -d, --debug			Show symbol/reloc cloning decisions
    -S, --short-circuit=STEP	Start at build step (requires prior --keep-tmp)
-				   1|orig	Build original kernel (default)
-				   2|patched	Build patched kernel
-				   3|diff	Diff objects
-				   4|kmod	Build patch module
+				   1|orig		Build original kernel (default)
+				   2|patched		Build patched kernel
+				   3|checksum		Generate checksums
+				   4|diff		Diff objects
+				   5|kmod		Build patch module
    -T, --keep-tmp		Preserve tmp dir on exit
 
 EOF
@@ -203,10 +206,11 @@ process_args() {
 				[[ ! -d "$TMP_DIR" ]] && die "--short-circuit requires preserved klp-tmp dir"
 				keep_tmp=1
 				case "$2" in
-					1 | orig)	SHORT_CIRCUIT=1; ;;
-					2 | patched)	SHORT_CIRCUIT=2; ;;
-					3 | diff)	SHORT_CIRCUIT=3; ;;
-					4 | mod)	SHORT_CIRCUIT=4; ;;
+					1 | orig)		SHORT_CIRCUIT=1; ;;
+					2 | patched)		SHORT_CIRCUIT=2; ;;
+					3 | checksum)		SHORT_CIRCUIT=3; ;;
+					4 | diff)		SHORT_CIRCUIT=4; ;;
+					5 | kmod)		SHORT_CIRCUIT=5; ;;
 					*)		die "invalid short-circuit step '$2'" ;;
 				esac
 				shift 2
@@ -513,11 +517,8 @@ clean_kernel() {
 build_kernel() {
 	local build="$1"
 	local log="$TMP_DIR/build.log"
-	local objtool_args=()
 	local cmd=()
 
-	objtool_args=("--checksum")
-
 	cmd=("make")
 
 	# When a patch to a kernel module references a newly created unexported
@@ -544,7 +545,6 @@ build_kernel() {
 	fi
 	cmd+=("-j$JOBS")
 	cmd+=("KCFLAGS=-ffunction-sections -fdata-sections")
-	cmd+=("OBJTOOL_ARGS=${objtool_args[*]}")
 	cmd+=("vmlinux")
 	cmd+=("modules")
 
@@ -574,7 +574,7 @@ copy_orig_objects() {
 
 	find_objects | mapfile -t files
 
-	xtrace_save "copying orig objects"
+	xtrace_save "copying original objects"
 	for _file in "${files[@]}"; do
 		local rel_file="${_file/.ko/.o}"
 		local file="$PWD/$rel_file"
@@ -630,6 +630,35 @@ copy_patched_objects() {
 	mv -f "$TMP_DIR/build.log" "$PATCHED_DIR"
 }
 
+# Copy .o files to a separate directory and run "objtool klp checksum" on each
+# copy.  The checksums are written to a .discard.sym_checksum section.
+#
+# If match_dir is given, only process files which also exist there.
+generate_checksums() {
+	local src_dir="$1"
+	local dest_dir="$2"
+	local match_dir="${3:-}"
+	local files=()
+	local file
+
+	rm -rf "$dest_dir"
+	mkdir -p "$dest_dir"
+
+	find "$src_dir" -type f -name "*.o" | mapfile -t files
+	for file in "${files[@]}"; do
+		local rel="${file#"$src_dir"/}"
+		local dest="$dest_dir/$rel"
+
+		[[ -n "$match_dir" && ! -f "$match_dir/$rel" ]] && continue
+
+		mkdir -p "$(dirname "$dest")"
+		cp -f "$file" "$dest"
+		"$SRC/tools/objtool/objtool" klp checksum "$dest"
+	done
+
+	touch "$dest_dir/.complete"
+}
+
 # Diff changed objects, writing output object to $DIFF_DIR
 diff_objects() {
 	local log="$KLP_DIFF_LOG"
@@ -639,16 +668,16 @@ diff_objects() {
 	rm -rf "$DIFF_DIR"
 	mkdir -p "$DIFF_DIR"
 
-	find "$PATCHED_DIR" -type f -name "*.o" | mapfile -t files
+	find "$PATCHED_CSUM_DIR" -type f -name "*.o" | mapfile -t files
 	[[ ${#files[@]} -eq 0 ]] && die "no changes detected"
 
 	[[ -v DEBUG_CLONE ]] && opts=("--debug")
 
 	# Diff all changed objects
 	for file in "${files[@]}"; do
-		local rel_file="${file#"$PATCHED_DIR"/}"
+		local rel_file="${file#"$PATCHED_CSUM_DIR"/}"
 		local orig_file="$rel_file"
-		local patched_file="$PATCHED_DIR/$rel_file"
+		local patched_file="$PATCHED_CSUM_DIR/$rel_file"
 		local out_file="$DIFF_DIR/$rel_file"
 		local filter=()
 		local cmd=()
@@ -672,7 +701,7 @@ diff_objects() {
 		fi
 
 		(
-			cd "$ORIG_DIR"
+			cd "$ORIG_CSUM_DIR"
 			[[ -v VERBOSE ]] && echo "${cmd[@]}"
 			"${cmd[@]}"							\
 				1> >(tee -a "$log")					\
@@ -682,9 +711,9 @@ diff_objects() {
 	done
 }
 
-# For each changed object, run objtool with --debug-checksum to get the
-# per-instruction checksums, and then diff those to find the first changed
-# instruction for each function.
+# For each changed object, run "objtool klp checksum" with --debug-checksum to
+# get the per-instruction checksums, and then diff those to find the first
+# changed instruction for each function.
 diff_checksums() {
 	local orig_log="$ORIG_DIR/checksum.log"
 	local patched_log="$PATCHED_DIR/checksum.log"
@@ -709,8 +738,7 @@ diff_checksums() {
 	done
 
 	cmd=("$OBJTOOL")
-	cmd+=("--checksum")
-	cmd+=("--link")
+	cmd+=("klp" "checksum")
 	cmd+=("--dry-run")
 
 	for file in "${!funcs[@]}"; do
@@ -719,11 +747,11 @@ diff_checksums() {
 		(
 			cd "$ORIG_DIR"
 			"${cmd[@]}" "$opt" "$file" &> "$orig_log" || \
-				( cat "$orig_log" >&2; die "objtool --debug-checksum failed" )
+				( cat "$orig_log" >&2; die "objtool klp checksum failed" )
 
 			cd "$PATCHED_DIR"
 			"${cmd[@]}" "$opt" "$file" &> "$patched_log" ||	\
-				( cat "$patched_log" >&2; die "objtool --debug-checksum failed" )
+				( cat "$patched_log" >&2; die "objtool klp checksum failed" )
 		)
 
 		for func in ${funcs[$file]}; do
@@ -861,6 +889,13 @@ if (( SHORT_CIRCUIT <= 2 )); then
 fi
 
 if (( SHORT_CIRCUIT <= 3 )); then
+	status "Generating original checksums"
+	generate_checksums "$ORIG_DIR" "$ORIG_CSUM_DIR" "$PATCHED_DIR"
+	status "Generating patched checksums"
+	generate_checksums "$PATCHED_DIR" "$PATCHED_CSUM_DIR"
+fi
+
+if (( SHORT_CIRCUIT <= 4 )); then
 	status "Diffing objects"
 	diff_objects
 	if [[ -v DIFF_CHECKSUM ]]; then
@@ -869,7 +904,7 @@ if (( SHORT_CIRCUIT <= 3 )); then
 	fi
 fi
 
-if (( SHORT_CIRCUIT <= 4 )); then
+if (( SHORT_CIRCUIT <= 5 )); then
 	status "Building patch module: $OUTFILE"
 	build_patch_module
 fi
-- 
2.53.0

[PATCH v2 43/53] objtool/klp: Remove "objtool --checksum"

[Josh Poimboeuf]

The checksum functionality has been moved to "objtool klp checksum"
which is now used by klp-build.  Remove the now-dead --checksum and
--debug-checksum options from the default objtool command.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 scripts/livepatch/klp-build   |  5 ++++-
 tools/objtool/builtin-check.c | 17 +----------------
 tools/objtool/check.c         | 10 ----------
 3 files changed, 5 insertions(+), 27 deletions(-)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index 8a4b268261a6..f8a80ad0f829 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -275,6 +275,9 @@ validate_config() {
 		[[ "$CONFIG_AS_VERSION" -lt 200000 ]] &&	\
 		die "Clang assembler version < 20 not supported"
 
+	"$OBJTOOL" klp 2>&1 | command grep -q "not implemented" && \
+		die "objtool not built with KLP support; install xxhash-devel/libxxhash-dev (version >= 0.8) and recompile"
+
 	return 0
 }
 
@@ -653,7 +656,7 @@ generate_checksums() {
 
 		mkdir -p "$(dirname "$dest")"
 		cp -f "$file" "$dest"
-		"$SRC/tools/objtool/objtool" klp checksum "$dest"
+		"$OBJTOOL" klp checksum "$dest"
 	done
 
 	touch "$dest_dir/.complete"
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index b780df513715..ec7f10a5ef19 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -73,7 +73,6 @@ static int parse_hacks(const struct option *opt, const char *str, int unset)
 
 static const struct option check_options[] = {
 	OPT_GROUP("Actions:"),
-	OPT_BOOLEAN(0,		 "checksum", &opts.checksum, "generate per-function checksums"),
 	OPT_BOOLEAN(0,		 "cfi", &opts.cfi, "annotate kernel control flow integrity (kCFI) function preambles"),
 	OPT_STRING_OPTARG('d',	 "disas", &opts.disas, "function-pattern", "disassemble functions", "*"),
 	OPT_CALLBACK_OPTARG('h', "hacks", NULL, NULL, "jump_label,noinstr,skylake", "patch toolchain bugs/limitations", parse_hacks),
@@ -95,7 +94,6 @@ static const struct option check_options[] = {
 	OPT_GROUP("Options:"),
 	OPT_BOOLEAN(0,		 "backtrace", &opts.backtrace, "unwind on error"),
 	OPT_BOOLEAN(0,		 "backup", &opts.backup, "create backup (.orig) file on warning/error"),
-	OPT_STRING(0,		 "debug-checksum", &opts.debug_checksum,  "funcs", "enable checksum debug output"),
 	OPT_BOOLEAN(0,		 "dry-run", &opts.dryrun, "don't write modifications"),
 	OPT_BOOLEAN(0,		 "link", &opts.link, "object is a linked object"),
 	OPT_BOOLEAN(0,		 "module", &opts.module, "object is part of a kernel module"),
@@ -165,20 +163,7 @@ static bool opts_valid(void)
 		return false;
 	}
 
-#ifndef BUILD_KLP
-	if (opts.checksum) {
-		ERROR("--checksum not supported; install xxhash-devel/libxxhash-dev (version >= 0.8) and recompile");
-		return false;
-	}
-#endif
-
-	if (opts.debug_checksum && !opts.checksum) {
-		ERROR("--debug-checksum requires --checksum");
-		return false;
-	}
-
-	if (opts.checksum		||
-	    opts.disas			||
+	if (opts.disas			||
 	    opts.hack_jump_label	||
 	    opts.hack_noinstr		||
 	    opts.ibt			||
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 3e5d335d0e29..ae047be919c5 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -18,7 +18,6 @@
 #include <objtool/special.h>
 #include <objtool/trace.h>
 #include <objtool/warn.h>
-#include <objtool/checksum.h>
 #include <objtool/util.h>
 
 #include <linux/objtool_types.h>
@@ -4946,15 +4945,6 @@ int check(struct objtool_file *file)
 	if (opts.noabs)
 		warnings += check_abs_references(file);
 
-	if (opts.checksum) {
-		ret = calculate_checksums(file);
-		if (ret)
-			goto out;
-		ret = create_sym_checksum_section(file);
-		if (ret)
-			goto out;
-	}
-
 	if (opts.orc && nr_insns) {
 		ret = orc_create(file);
 		if (ret)
-- 
2.53.0

[PATCH v2 44/53] klp-build: Validate short-circuit prerequisites

[Josh Poimboeuf]

The --short-circuit option implicitly requires that certain directories
are already in klp-tmp.  Enforce that to prevent confusing errors.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 scripts/livepatch/klp-build | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index f8a80ad0f829..3adb2a7fd9c1 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -437,6 +437,20 @@ do_init() {
 	# builds in pwd.
 	[[ ! "$PWD" -ef "$SCRIPT_DIR/../.." ]] && die "please run from the kernel root directory"
 
+	if (( SHORT_CIRCUIT >= 2 )); then
+		[[ -f "$ORIG_DIR/.complete" ]] || die "-S $SHORT_CIRCUIT requires completed $ORIG_DIR"
+	fi
+	if (( SHORT_CIRCUIT >= 3 )); then
+		[[ -f "$PATCHED_DIR/.complete" ]] || die "-S $SHORT_CIRCUIT requires completed $PATCHED_DIR"
+	fi
+	if (( SHORT_CIRCUIT >= 4 )); then
+		[[ -f "$ORIG_CSUM_DIR/.complete" ]] || die "-S $SHORT_CIRCUIT requires completed $ORIG_CSUM_DIR"
+		[[ -f "$PATCHED_CSUM_DIR/.complete" ]] || die "-S $SHORT_CIRCUIT requires completed $PATCHED_CSUM_DIR"
+	fi
+	if (( SHORT_CIRCUIT >= 5 )); then
+		[[ -f "$DIFF_DIR/.complete" ]] || die "-S $SHORT_CIRCUIT requires completed $DIFF_DIR"
+	fi
+
 	(( SHORT_CIRCUIT <= 1 )) && rm -rf "$TMP_DIR"
 	mkdir -p "$TMP_DIR"
 
@@ -593,6 +607,7 @@ copy_orig_objects() {
 
 	mv -f "$TMP_DIR/build.log" "$ORIG_DIR"
 	touch "$TIMESTAMP"
+	touch "$ORIG_DIR/.complete"
 }
 
 # Copy all changed objects to $PATCHED_DIR
@@ -631,6 +646,7 @@ copy_patched_objects() {
 	(( found == 0 )) && die "no changes detected"
 
 	mv -f "$TMP_DIR/build.log" "$PATCHED_DIR"
+	touch "$PATCHED_DIR/.complete"
 }
 
 # Copy .o files to a separate directory and run "objtool klp checksum" on each
@@ -712,6 +728,8 @@ diff_objects() {
 				die "objtool klp diff failed"
 		)
 	done
+
+	touch "$DIFF_DIR/.complete"
 }
 
 # For each changed object, run "objtool klp checksum" with --debug-checksum to
-- 
2.53.0

Re: [PATCH v2 44/53] klp-build: Validate short-circuit prerequisites

[Song Liu]

On Fri, May 1, 2026 at 5:09 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> The --short-circuit option implicitly requires that certain directories
> are already in klp-tmp.  Enforce that to prevent confusing errors.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

[PATCH v2 45/53] objtool/klp: Calculate object checksums

[Josh Poimboeuf]

Start checksumming data objects in preparation for revamping the
correlation algorithm.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/include/objtool/checksum.h | 44 ++++++++----
 tools/objtool/include/objtool/warn.h     | 29 ++++----
 tools/objtool/klp-checksum.c             | 89 +++++++++++++++++++-----
 tools/objtool/klp-diff.c                 |  2 +-
 4 files changed, 117 insertions(+), 47 deletions(-)

diff --git a/tools/objtool/include/objtool/checksum.h b/tools/objtool/include/objtool/checksum.h
index be4eb7dfe6f2..d46293f54716 100644
--- a/tools/objtool/include/objtool/checksum.h
+++ b/tools/objtool/include/objtool/checksum.h
@@ -6,28 +6,44 @@
 
 #ifdef BUILD_KLP
 
-static inline void checksum_init(struct symbol *func)
+static inline void checksum_init(struct symbol *sym)
 {
-	if (func && !func->csum.state) {
-		func->csum.state = XXH3_createState();
-		XXH3_64bits_reset(func->csum.state);
+	if (sym && !sym->csum.state) {
+		sym->csum.state = XXH3_createState();
+		XXH3_64bits_reset(sym->csum.state);
 	}
 }
 
-static inline void checksum_update(struct symbol *func,
-				   struct instruction *insn,
-				   const void *data, size_t size)
+static inline void __checksum_update(struct symbol *sym, const void *data,
+				     size_t size)
 {
-	XXH3_64bits_update(func->csum.state, data, size);
-	dbg_checksum(func, insn, XXH3_64bits_digest(func->csum.state));
+	XXH3_64bits_update(sym->csum.state, data, size);
 }
 
-static inline void checksum_finish(struct symbol *func)
+static inline void __checksum_update_insn(struct symbol *sym,
+					  struct instruction *insn,
+					  const void *data, size_t size)
 {
-	if (func && func->csum.state) {
-		func->csum.checksum = XXH3_64bits_digest(func->csum.state);
-		XXH3_freeState(func->csum.state);
-		func->csum.state = NULL;
+	__checksum_update(sym, data, size);
+	dbg_checksum_insn(sym, insn, XXH3_64bits_digest(sym->csum.state));
+}
+
+static inline void __checksum_update_object(struct symbol *sym,
+					    unsigned long offset,
+					    const char *what, const void *data,
+					    size_t size)
+{
+	__checksum_update(sym, &offset, sizeof(offset));
+	__checksum_update(sym, data, size);
+	dbg_checksum_object(sym, offset, what, XXH3_64bits_digest(sym->csum.state));
+}
+
+static inline void checksum_finish(struct symbol *sym)
+{
+	if (sym && sym->csum.state) {
+		sym->csum.checksum = XXH3_64bits_digest(sym->csum.state);
+		XXH3_freeState(sym->csum.state);
+		sym->csum.state = NULL;
 	}
 }
 
diff --git a/tools/objtool/include/objtool/warn.h b/tools/objtool/include/objtool/warn.h
index fa8b7d292e83..595ee8009667 100644
--- a/tools/objtool/include/objtool/warn.h
+++ b/tools/objtool/include/objtool/warn.h
@@ -130,10 +130,22 @@ static inline void unindent(int *unused) { indent--; }
 		objname ? ": " : "",					\
 		##__VA_ARGS__)
 
-#define dbg(args...)							\
+#define dbg_checksum_insn(func, insn, checksum)				\
 ({									\
-	if (unlikely(debug))						\
-		__dbg(args);						\
+	if (unlikely(func->debug_checksum)) {				\
+		char *insn_off = offstr(insn->sec, insn->offset);	\
+		__dbg("checksum: %s(): %s %016llx",			\
+		      func->name, insn_off, (unsigned long long)checksum);\
+		free(insn_off);						\
+	}								\
+})
+
+#define dbg_checksum_object(sym, offset, what, checksum)		\
+({									\
+	if (unlikely(sym->debug_checksum))				\
+		__dbg("checksum: %s+0x%lx: %s %016llx",			\
+		      sym->name, offset, what,				\
+		      (unsigned long long)checksum);			\
 })
 
 #define __dbg_indent(format, ...)					\
@@ -147,15 +159,4 @@ static inline void unindent(int *unused) { indent--; }
 	__dbg_indent(args);						\
 	indent++
 
-#define dbg_checksum(func, insn, checksum)				\
-({									\
-	if (unlikely(insn->sym && insn->sym->pfunc &&			\
-		     insn->sym->pfunc->debug_checksum)) {		\
-		char *insn_off = offstr(insn->sec, insn->offset);	\
-		__dbg("checksum: %s %s %016llx",			\
-		      func->name, insn_off, (unsigned long long)checksum);\
-		free(insn_off);						\
-	}								\
-})
-
 #endif /* _WARN_H */
diff --git a/tools/objtool/klp-checksum.c b/tools/objtool/klp-checksum.c
index e4a910f3211c..19653dbe109d 100644
--- a/tools/objtool/klp-checksum.c
+++ b/tools/objtool/klp-checksum.c
@@ -35,7 +35,7 @@ static int checksum_debug_init(struct objtool_file *file)
 			*comma = '\0';
 
 		for_each_sym_by_name(file->elf, s, sym) {
-			if (!is_func_sym(sym))
+			if (!is_func_sym(sym) && !is_object_sym(sym))
 				continue;
 			sym->debug_checksum = 1;
 			found = true;
@@ -66,14 +66,14 @@ static void checksum_update_insn(struct objtool_file *file, struct symbol *func,
 	if (insn->fake)
 		return;
 
-	checksum_update(func, insn, insn->sec->data->d_buf + insn->offset, insn->len);
+	__checksum_update_insn(func, insn, insn->sec->data->d_buf + insn->offset, insn->len);
 
 	if (!reloc) {
 		struct symbol *call_dest = insn_call_dest(insn);
 
 		if (call_dest)
-			checksum_update(func, insn, call_dest->demangled_name,
-					strlen(call_dest->demangled_name));
+			__checksum_update_insn(func, insn, call_dest->demangled_name,
+					       strlen(call_dest->demangled_name));
 		goto alts;
 	}
 
@@ -84,7 +84,7 @@ static void checksum_update_insn(struct objtool_file *file, struct symbol *func,
 		char *str;
 
 		str = sym->sec->data->d_buf + sym->offset + offset;
-		checksum_update(func, insn, str, strlen(str));
+		__checksum_update_insn(func, insn, str, strlen(str));
 		goto alts;
 	}
 
@@ -96,8 +96,9 @@ static void checksum_update_insn(struct objtool_file *file, struct symbol *func,
 		offset -= sym->offset;
 	}
 
-	checksum_update(func, insn, sym->demangled_name, strlen(sym->demangled_name));
-	checksum_update(func, insn, &offset, sizeof(offset));
+	__checksum_update_insn(func, insn, sym->demangled_name,
+			       strlen(sym->demangled_name));
+	__checksum_update_insn(func, insn, &offset, sizeof(offset));
 
 alts:
 	for (alt = insn->alts; alt; alt = alt->next) {
@@ -108,12 +109,13 @@ static void checksum_update_insn(struct objtool_file *file, struct symbol *func,
 			break;
 		in_alt = true;
 
-		checksum_update(func, insn, &alt->type, sizeof(alt->type));
+		__checksum_update_insn(func, insn, &alt->type,
+				       sizeof(alt->type));
 
 		if (alt_group && alt_group->orig_group) {
 			struct instruction *alt_insn;
 
-			checksum_update(func, insn, &alt_group->feature, sizeof(alt_group->feature));
+			__checksum_update_insn(func, insn, &alt_group->feature,sizeof(alt_group->feature));
 
 			for (alt_insn = alt->insn; alt_insn; alt_insn = next_insn_same_sec(file, alt_insn)) {
 				checksum_update_insn(file, func, alt_insn);
@@ -128,31 +130,82 @@ static void checksum_update_insn(struct objtool_file *file, struct symbol *func,
 	}
 }
 
+static void checksum_update_object(struct objtool_file *file, struct symbol *sym)
+{
+	struct reloc *reloc;
+
+	__checksum_update_object(sym, 0, "len", &sym->len, sizeof(sym->len));
+
+	if (sym->sec->data->d_buf)
+		__checksum_update_object(sym, 0, "data",
+					 sym->sec->data->d_buf + sym->offset,
+					 sym->len);
+
+	sym_for_each_reloc(file->elf, sym, reloc) {
+		unsigned long sym_offset = reloc_offset(reloc) - sym->offset;
+		struct symbol *target = reloc->sym;
+		s64 offset;
+
+		offset = reloc_addend(reloc);
+
+		if (is_string_sec(target->sec)) {
+			char *str;
+
+			str = target->sec->data->d_buf + target->offset + offset;
+			__checksum_update_object(sym, sym_offset,
+						 "reloc string", str, strlen(str));
+			continue;
+		}
+
+		if (is_sec_sym(target)) {
+			target = find_symbol_containing(reloc->sym->sec, offset);
+			if (!target)
+				continue;
+
+			offset -= target->offset;
+		}
+
+		__checksum_update_object(sym, sym_offset, "reloc name",
+					 target->demangled_name,
+					 strlen(target->demangled_name));
+		__checksum_update_object(sym, sym_offset, "reloc addend",
+					 &offset, sizeof(offset));
+	}
+}
+
 int calculate_checksums(struct objtool_file *file)
 {
 	struct instruction *insn;
-	struct symbol *func;
+	struct symbol *sym;
 
 	if (checksum_debug_init(file))
 		return -1;
 
-	for_each_sym(file->elf, func) {
+	for_each_sym(file->elf, sym) {
+
 		/*
 		 * Skip cold subfunctions and aliases: they share the
 		 * parent's checksum via func_for_each_insn() which
 		 * follows func->cfunc into the cold subfunction.
 		 */
-		if (!is_func_sym(func) || is_cold_func(func) ||
-		    is_alias_sym(func) || !func->len)
+		if (is_cold_func(sym) || is_alias_sym(sym) || !sym->len ||
+		    !sym->sec || !sym->sec->data)
 			continue;
 
-		checksum_init(func);
+		if (is_func_sym(sym)) {
+			checksum_init(sym);
+			func_for_each_insn(file, sym, insn)
+				checksum_update_insn(file, sym, insn);
+			checksum_finish(sym);
 
-		func_for_each_insn(file, func, insn)
-			checksum_update_insn(file, func, insn);
+		} else if (is_object_sym(sym)) {
+			checksum_init(sym);
+			checksum_update_object(file, sym);
+			checksum_finish(sym);
+		}
 
-		checksum_finish(func);
 	}
+
 	return 0;
 }
 
@@ -213,7 +266,7 @@ int cmd_klp_checksum(int argc, const char **argv)
 	int ret;
 
 	const struct option options[] = {
-		OPT_STRING(0,	"debug-checksum", &opts.debug_checksum,	"funcs", "enable checksum debug output"),
+		OPT_STRING(0,	"debug-checksum", &opts.debug_checksum,	"syms", "enable checksum debug output"),
 		OPT_BOOLEAN(0,	"dry-run", &opts.dryrun, "don't write modifications"),
 		OPT_END(),
 	};
diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 95359ad336bb..5f13d759e02f 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -201,7 +201,7 @@ static int read_sym_checksums(struct elf *elf)
 			return -1;
 		}
 
-		if (is_func_sym(sym))
+		if (is_func_sym(sym) || is_object_sym(sym))
 			sym->csum.checksum = sym_checksum->checksum;
 	}
 
-- 
2.53.0

Re: [PATCH v2 45/53] objtool/klp: Calculate object checksums

[Song Liu]

On Fri, May 1, 2026 at 5:09 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> Start checksumming data objects in preparation for revamping the
> correlation algorithm.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

[PATCH v2 46/53] objtool/klp: Rewrite symbol correlation algorithm

[Josh Poimboeuf]

Rewrite the symbol correlation code, using a tiered list of
deterministic strategies in a loop.  For duplicately named symbols, each
tier applies a filter with the goal of finding a 1:1 deterministic
correlation between the original and patched version of the symbol.

The three matching strategies are:

  find_twin(): A funnel of progressively tighter filters.  Candidates
  with the same demangled name are counted at four levels: name, scope
  (local-vs-global), file (strict file association), and checksum
  (unchanged functions).  The widest level that yields a 1:1 match wins,
  narrower levels are only tried when the wider level is ambiguous.

  find_twin_suffixed(): Uses already-correlated LLVM symbol pairs to map
  .llvm.<hash> suffixes from orig to patched.  Because all promoted
  symbols from the same TU share the same hash, one correlated pair
  seeds the mapping for the entire TU.

  find_twin_positional(): Last resort, matches symbols by position among
  same-named candidates, similar to livepatch sympos.  Used for data
  objects like __quirk variables where no deterministic filter can
  distinguish the candidates.

Overall this works much better than the existing algorithm, particularly
with LTO kernels.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/klp-diff.c | 521 +++++++++++++++++++++++++++++----------
 1 file changed, 385 insertions(+), 136 deletions(-)

diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index 5f13d759e02f..a9c993298b82 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -408,78 +408,358 @@ static bool dont_correlate(struct symbol *sym)
 	       is_special_section_aux(sym->sec);
 }
 
-/*
- * When there is no full name match, try match demangled_name. This would
- * match original foo.llvm.123 to patched foo.llvm.456.
- *
- * Note that, in very rare cases, it is possible to have multiple
- * foo.llvm.<hash> in the same kernel. When this happens, report error and
- * fail the diff.
- */
-static int find_global_symbol_by_demangled_name(struct elf *elf, struct symbol *sym,
-						struct symbol **out_sym)
+static const char *llvm_suffix(const char *name)
 {
-	struct symbol *sym2, *result = NULL;
-	int count = 0;
+	return strstr(name, ".llvm.");
+}
 
-	for_each_sym_by_demangled_name(elf, sym->demangled_name, sym2) {
-		if (is_local_sym(sym2) || sym2->twin)
+static bool is_llvm_sym(struct symbol *sym)
+{
+	return llvm_suffix(sym->name);
+}
+
+/*
+ * Determine if two symbols have compatible source file origins:
+ *
+ *   - If both symbols are local, only return true if they belong to the same
+ *     ELF file symbol.
+ *
+ *   - If both symbols are global, always return true, as globals don't have
+ *     file associations.
+ *
+ *   - If they have different scopes, also return true, as the patch might have
+ *     changed the symbol's scope.
+ *
+ * Works for both same-ELF (direct pointer compare) and cross-ELF
+ * (compare via file->twin) cases.
+ */
+static bool maybe_same_file(struct symbol *sym1, struct symbol *sym2)
+{
+	if (!sym1->file || !sym2->file)
+		return true;
+	if (sym1->file == sym2->file)
+		return true;
+	return sym1->file->twin == sym2->file;
+}
+
+/*
+ * Similar to maybe_same_file(), but strict: no scope changes allowed.
+ *
+ * Works for both same-ELF (direct pointer compare) and cross-ELF
+ * (compare via file->twin) cases.
+ */
+static bool same_file(struct symbol *sym1, struct symbol *sym2)
+{
+	if (llvm_suffix(sym1->name) && llvm_suffix(sym2->name))
+		return true;
+	if (!sym1->file && !sym2->file)
+		return true;
+	if (!sym1->file || !sym2->file)
+		return false;
+	if (sym1->file == sym2->file)
+		return true;
+	return sym1->file->twin == sym2->file;
+}
+
+/*
+ * Is it a local symbol, or at least was it local in the translation unit
+ * before LLVM promoted it?
+ */
+static bool is_tu_local_sym(struct symbol *sym)
+{
+	return is_local_sym(sym) || is_llvm_sym(sym);
+}
+
+/*
+ * Try to find sym1's twin in patched using deterministic matching.
+ *
+ * Multiple symbols can share a demangled name (e.g., static functions in
+ * different TUs).  This function counts same-named candidates through a
+ * funnel of progressively tighter filters.  Each level is a strict subset
+ * of the previous one.
+ *
+ * The widest level that yields a 1:1 match wins.  Narrower levels are only
+ * needed when the wider level is ambiguous (count > 1).
+ *
+ * Candidates are pre-filtered by maybe_same_file(), which narrows most
+ * local symbols to their own TU.  For example, 19 different static
+ * type_show() functions across vmlinux.o each see only one candidate after
+ * pre-filtering, so they match immediately at Level 1.
+ *
+ * Level 1 (name): Works when the demangled name is unique after
+ * pre-filtering.  Handles most symbols: unique globals like copy_signal(),
+ * or per-TU locals like pcspkr_probe().
+ *
+ * Level 2 (scope): Filters by local-vs-global (TU-local-vs-not).  Example:
+ * parse_header() exists as both a static and a global function.  Level 1
+ * sees both (same demangled name), but Level 2 separates them by scope.
+ *
+ * Level 3 (file): Strict file matching via same_file(), which rejects scope
+ * changes.  Example: LLVM-promoted foo.llvm.12345 (global, no FILE symbol)
+ * vs genuine local foo (has FILE symbol).  Both are TU-local so Level 2
+ * can't distinguish them, but same_file() rejects the pair because one has
+ * a file association and the other doesn't.
+ *
+ * Level 4 (checksum): Distinguishes by function checksum.  Example:
+ * usb_devnode.llvm.AAA and usb_devnode.llvm.BBB are two LLVM-promoted
+ * functions from different TUs with the same demangled name.  After a TU
+ * change, the .llvm. hashes change but the functions themselves may be
+ * unchanged.  Level 4 matches each to the patched candidate with the
+ * same checksum.
+ */
+static struct symbol *find_twin(struct elfs *e, struct symbol *sym1)
+{
+	struct symbol *name_last = NULL, *scope_last = NULL,
+		      *file_last = NULL, *csum_last = NULL;
+	unsigned int name_orig = 0, name_patched = 0;
+	unsigned int scope_orig = 0, scope_patched = 0;
+	unsigned int file_orig = 0, file_patched = 0;
+	unsigned int csum_orig = 0, csum_patched = 0;
+	struct symbol *sym2, *match = NULL;
+
+	/* Count orig candidates */
+	for_each_sym_by_demangled_name(e->orig, sym1->demangled_name, sym2) {
+		if (sym2->twin || sym1->type != sym2->type || dont_correlate(sym2) ||
+		    (!maybe_same_file(sym1, sym2)))
 			continue;
 
-		count++;
-		result = sym2;
+		/* Level 1: name match (widest filter)  */
+		name_orig++;
+
+		/* Level 2: scope (scope changes allowed) */
+		if (is_tu_local_sym(sym1) != is_tu_local_sym(sym2))
+			continue;
+		scope_orig++;
+
+		/* Level 3: file (scope changes disallowed) */
+		if (!same_file(sym1, sym2))
+			continue;
+		file_orig++;
+
+		/* Level 4: checksum (unchanged symbols) */
+		if (sym1->len != sym2->len || !sym1->csum.checksum ||
+		    sym1->csum.checksum != sym2->csum.checksum)
+			continue;
+		csum_orig++;
 	}
 
-	if (count > 1) {
-		ERROR("Multiple (%d) correlation candidates for %s", count, sym->name);
-		return -1;
+	/* Count patched candidates */
+	for_each_sym_by_demangled_name(e->patched, sym1->demangled_name, sym2) {
+		if (sym2->twin || sym1->type != sym2->type || dont_correlate(sym2) ||
+		    !maybe_same_file(sym1, sym2))
+			continue;
+
+		/* Level 1 */
+		name_patched++;
+		name_last = sym2;
+
+		/* Level 2 */
+		if (is_tu_local_sym(sym1) != is_tu_local_sym(sym2))
+			continue;
+		scope_patched++;
+		scope_last = sym2;
+
+		/* Level 3 */
+		if (!same_file(sym1, sym2))
+			continue;
+		file_patched++;
+		file_last = sym2;
+
+		/* Level 4 */
+		if (sym1->len != sym2->len || !sym1->csum.checksum ||
+		    sym1->csum.checksum != sym2->csum.checksum)
+			continue;
+		csum_patched++;
+		csum_last = sym2;
+	}
+
+	/* Return the widest level that yields a unique (1:1) match */
+	if (name_orig == 1 && name_patched == 1)
+		match = name_last;
+	else if (scope_orig == 1 && scope_patched == 1)
+		match = scope_last;
+	else if (file_orig == 1 && file_patched == 1)
+		match = file_last;
+	else if (csum_orig == 1 && csum_patched == 1)
+		match = csum_last;
+
+	return match;
+}
+
+struct llvm_suffix_pair {
+	struct hlist_node hash;
+	const char *orig;
+	const char *patched;
+};
+
+static DECLARE_HASHTABLE(suffix_map, 7);
+
+/*
+ * Build a mapping of known orig-to-patched LLVM suffixes based on
+ * already-correlated symbol pairs.  All promoted symbols from the same TU
+ * share the same .llvm.<hash> suffix, so one correlated pair seeds the map
+ * for the entire TU.
+ */
+static int update_suffix_map(struct elf *elf)
+{
+	struct llvm_suffix_pair *entry;
+	struct symbol *sym;
+
+	for_each_sym(elf, sym) {
+		const char *s1, *s2;
+		bool found;
+
+		if (!sym->twin)
+			continue;
+
+		s1 = llvm_suffix(sym->name);
+		s2 = llvm_suffix(sym->twin->name);
+
+		if (!s1 || !s2)
+			continue;
+
+		found = false;
+		hash_for_each_possible(suffix_map, entry, hash, str_hash(s1)) {
+			if (!strcmp(entry->orig, s1)) {
+				found = true;
+				break;
+			}
+		}
+		if (found)
+			continue;
+
+		entry = calloc(1, sizeof(*entry));
+		if (!entry) {
+			ERROR_GLIBC("calloc");
+			return -1;
+		}
+
+		entry->orig = s1;
+		entry->patched = s2;
+		hash_add(suffix_map, &entry->hash, str_hash(s1));
 	}
 
-	*out_sym = result;
 	return 0;
 }
 
 /*
- * For each symbol in the original kernel, find its corresponding "twin" in the
- * patched kernel.
+ * Match by translating the symbol's .llvm.<hash> suffix through the suffix
+ * map to find the corresponding hash suffix for the patched object.
+ *
+ * Example: In the original kernel, TU drivers/base/core.c contains
+ * foo.llvm.12345 and bar.llvm.12345 (same TU, same hash).  After patching,
+ * they become foo.llvm.67890 and bar.llvm.67890.  If foo was already
+ * correlated by find_twin() (e.g., unique by name), the suffix map records
+ * .llvm.12345 -> .llvm.67890.  When processing bar.llvm.12345, this
+ * function looks up .llvm.12345, gets .llvm.67890, constructs the name
+ * bar.llvm.67890, and finds the match.
+ */
+static struct symbol *find_twin_suffixed(struct elf *elf, struct symbol *sym1)
+{
+	const char *suffix, *patched_suffix = NULL;
+	struct symbol *sym2, *match = NULL;
+	char name[SYM_NAME_LEN];
+	struct llvm_suffix_pair *entry;
+	int count = 0;
+
+	suffix = llvm_suffix(sym1->name);
+	if (!suffix)
+		return NULL;
+
+	hash_for_each_possible(suffix_map, entry, hash, str_hash(suffix)) {
+		if (!strcmp(entry->orig, suffix)) {
+			patched_suffix = entry->patched;
+			break;
+		}
+	}
+	if (!patched_suffix)
+		return NULL;
+
+	if (snprintf_check(name, SYM_NAME_LEN, "%s%s",
+			   sym1->demangled_name, patched_suffix))
+		return NULL;
+
+	for_each_sym_by_name(elf, name, sym2) {
+		if (sym2->twin || sym1->type != sym2->type || dont_correlate(sym2))
+			continue;
+		count++;
+		match = sym2;
+	}
+
+	if (count == 1)
+		return match;
+
+	return NULL;
+}
+
+/*
+ * Last-resort positional matching.
+ *
+ * Finds a symbol with the same position in the symbol table among
+ * same-demangled-name candidates, similar to livepatch sympos.  Note that
+ * LLVM-promoted symbols are globals, which come after locals in the symbol
+ * table, so we have to be careful not to compare different scopes.
+ *
+ * Example: arch/x86/events/intel/core.c defines many __quirk variables via
+ * X86_MATCH_*() macros.  In the symbol table they appear as __quirk.90,
+ * __quirk.97, __quirk.101, etc., all with demangled name __quirk, same
+ * scope, and same FILE symbol.  No deterministic filter can distinguish
+ * them, so they're matched by position: the 1st __quirk in orig matches the
+ * 1st in patched, the 2nd matches the 2nd, etc.
+ *
+ * This is less deterministic than the other strategies, so it's done last.
+ */
+static struct symbol *find_twin_positional(struct elfs *e, struct symbol *sym1)
+{
+	unsigned int idx_orig = 0, idx_patched = 0;
+	unsigned int sym1_pos = 0;
+	struct symbol *sym2, *match = NULL;
+
+	for_each_sym_by_demangled_name(e->orig, sym1->demangled_name, sym2) {
+		if (sym2->twin || sym1->type != sym2->type || dont_correlate(sym2) ||
+		    !maybe_same_file(sym1, sym2))
+			continue;
+		if (is_tu_local_sym(sym1) != is_tu_local_sym(sym2) ||
+		    is_llvm_sym(sym1) != is_llvm_sym(sym2))
+			continue;
+		if (sym1 == sym2)
+			sym1_pos = idx_orig;
+		idx_orig++;
+	}
+
+	for_each_sym_by_demangled_name(e->patched, sym1->demangled_name, sym2) {
+		if (sym2->twin || sym1->type != sym2->type || dont_correlate(sym2) ||
+		    !maybe_same_file(sym1, sym2))
+			continue;
+		if (is_tu_local_sym(sym1) != is_tu_local_sym(sym2) ||
+		    is_llvm_sym(sym1) != is_llvm_sym(sym2))
+			continue;
+		if (idx_patched == sym1_pos)
+			match = sym2;
+		idx_patched++;
+	}
+
+	if (idx_orig != idx_patched)
+		return NULL;
+
+	return match;
+}
+
+/*
+ * Correlate symbols between the orig and patched objects.  This is a
+ * prerequisite for detecting changed functions, as well as for properly
+ * translating relocations so they point to the correct symbol.
  */
 static int correlate_symbols(struct elfs *e)
 {
 	struct symbol *file1_sym, *file2_sym;
 	struct symbol *sym1, *sym2;
+	bool progress;
 
+	/* Correlate FILE symbols */
 	file1_sym = first_file_symbol(e->orig);
 	file2_sym = first_file_symbol(e->patched);
 
-	/*
-	 * Correlate any locals before the first FILE symbol.  This has been
-	 * seen when LTO inexplicably strips the initramfs_data.o FILE symbol
-	 * due to the file only containing data and no code.
-	 */
-	for_each_sym(e->orig, sym1) {
-		if (sym1 == file1_sym || !is_local_sym(sym1))
-			break;
-
-		if (dont_correlate(sym1))
-			continue;
-
-		for_each_sym(e->patched, sym2) {
-			if (sym2 == file2_sym || !is_local_sym(sym2))
-				break;
-
-			if (sym2->twin || dont_correlate(sym2))
-				continue;
-
-			if (strcmp(sym1->demangled_name, sym2->demangled_name))
-				continue;
-
-			sym1->twin = sym2;
-			sym2->twin = sym1;
-			break;
-		}
-	}
-
-	/* Correlate locals after the first FILE symbol */
 	for (; ; file1_sym = next_file_symbol(e->orig, file1_sym),
 		 file2_sym = next_file_symbol(e->patched, file2_sym)) {
 
@@ -503,92 +783,52 @@ static int correlate_symbols(struct elfs *e)
 
 		file1_sym->twin = file2_sym;
 		file2_sym->twin = file1_sym;
-
-		sym1 = file1_sym;
-
-		for_each_sym_continue(e->orig, sym1) {
-			if (is_file_sym(sym1) || !is_local_sym(sym1))
-				break;
-
-			if (dont_correlate(sym1))
-				continue;
-
-			sym2 = file2_sym;
-			for_each_sym_continue(e->patched, sym2) {
-				if (is_file_sym(sym2) || !is_local_sym(sym2))
-					break;
-
-				if (sym2->twin || dont_correlate(sym2))
-					continue;
-
-				if (strcmp(sym1->demangled_name, sym2->demangled_name))
-					continue;
-
-				sym1->twin = sym2;
-				sym2->twin = sym1;
-				break;
-			}
-		}
 	}
 
-	/* Correlate globals */
-	for_each_sym(e->orig, sym1) {
-		if (sym1->bind == STB_LOCAL)
-			continue;
-
-		sym2 = find_global_symbol_by_name(e->patched, sym1->name);
-		if (sym2 && !sym2->twin) {
-			sym1->twin = sym2;
-			sym2->twin = sym1;
-		}
-	}
 
 	/*
-	 * Correlate globals with demangled_name.
-	 * A separate loop is needed because we want to finish all the
-	 * full name correlations first.
+	 * Correlate in two phases: loop deterministic levels until no more
+	 * progress, then use positional fallback for the rest.  This prevents
+	 * the nondeterministic positional matching from stealing symbols that
+	 * have deterministic matches.
 	 */
+	hash_init(suffix_map);
+	do {
+		progress = false;
+		for_each_sym(e->orig, sym1) {
+			if (sym1->twin || dont_correlate(sym1))
+				continue;
+			sym2 = find_twin(e, sym1);
+			if (!sym2)
+				continue;
+			sym1->twin = sym2;
+			sym2->twin = sym1;
+			progress = true;
+		}
+
+		if (update_suffix_map(e->orig))
+			return -1;
+
+		for_each_sym(e->orig, sym1) {
+			if (sym1->twin || dont_correlate(sym1))
+				continue;
+			sym2 = find_twin_suffixed(e->patched, sym1);
+			if (!sym2)
+				continue;
+			sym1->twin = sym2;
+			sym2->twin = sym1;
+			progress = true;
+		}
+	} while (progress);
+
 	for_each_sym(e->orig, sym1) {
-		if (sym1->bind == STB_LOCAL || sym1->twin)
+		if (sym1->twin || dont_correlate(sym1))
 			continue;
-
-		if (find_global_symbol_by_demangled_name(e->patched, sym1, &sym2))
-			return -1;
-
-		if (sym2 && !sym2->twin) {
-			sym1->twin = sym2;
-			sym2->twin = sym1;
-		}
-	}
-
-	/* Correlate original locals with patched globals */
-	for_each_sym(e->orig, sym1) {
-		if (sym1->twin || dont_correlate(sym1) || !is_local_sym(sym1))
+		sym2 = find_twin_positional(e, sym1);
+		if (!sym2)
 			continue;
-
-		sym2 = find_global_symbol_by_name(e->patched, sym1->name);
-		if (!sym2 && find_global_symbol_by_demangled_name(e->patched, sym1, &sym2))
-			return -1;
-
-		if (sym2 && !sym2->twin) {
-			sym1->twin = sym2;
-			sym2->twin = sym1;
-		}
-	}
-
-	/* Correlate original globals with patched locals */
-	for_each_sym(e->patched, sym2) {
-		if (sym2->twin || dont_correlate(sym2) || !is_local_sym(sym2))
-			continue;
-
-		sym1 = find_global_symbol_by_name(e->orig, sym2->name);
-		if (!sym1 && find_global_symbol_by_demangled_name(e->orig, sym2, &sym1))
-			return -1;
-
-		if (sym1 && !sym1->twin) {
-			sym2->twin = sym1;
-			sym1->twin = sym2;
-		}
+		sym1->twin = sym2;
+		sym2->twin = sym1;
 	}
 
 	for_each_sym(e->orig, sym1) {
@@ -800,19 +1040,24 @@ static void mark_included_function(struct symbol *func)
  */
 static int mark_changed_functions(struct elfs *e)
 {
-	struct symbol *sym_orig, *patched_sym;
+	struct symbol *orig_sym, *patched_sym;
 	bool changed = false;
 
 	/* Find changed functions */
-	for_each_sym(e->orig, sym_orig) {
-		if (!is_func_sym(sym_orig) || dont_correlate(sym_orig))
+	for_each_sym(e->orig, orig_sym) {
+		if (dont_correlate(orig_sym))
 			continue;
 
-		patched_sym = sym_orig->twin;
+		patched_sym = orig_sym->twin;
 		if (!patched_sym)
 			continue;
 
-		if (sym_orig->csum.checksum != patched_sym->csum.checksum) {
+		if (orig_sym->csum.checksum != patched_sym->csum.checksum) {
+			if (!is_func_sym(orig_sym)) {
+				ERROR("changed data: %s", orig_sym->name);
+				return -1;
+			}
+
 			patched_sym->changed = 1;
 			mark_included_function(patched_sym);
 			changed = true;
@@ -837,7 +1082,7 @@ static int mark_changed_functions(struct elfs *e)
 			printf("%s: changed function: %s\n", objname, patched_sym->name);
 	}
 
-	return !changed ? -1 : 0;
+	return !changed ? 1 : 0;
 }
 
 static int clone_included_functions(struct elfs *e)
@@ -1870,6 +2115,7 @@ static int copy_import_ns(struct elfs *e)
 int cmd_klp_diff(int argc, const char **argv)
 {
 	struct elfs e = {0};
+	int ret;
 
 	argc = parse_options(argc, argv, klp_diff_options, klp_diff_usage, 0);
 	if (argc != 3)
@@ -1896,7 +2142,10 @@ int cmd_klp_diff(int argc, const char **argv)
 	if (correlate_symbols(&e))
 		return -1;
 
-	if (mark_changed_functions(&e))
+	ret = mark_changed_functions(&e);
+	if (ret < 0)
+		return -1;
+	if (ret > 0)
 		return 0;
 
 	e.out = elf_create_file(&e.orig->ehdr, argv[2]);
-- 
2.53.0

Re: [PATCH v2 46/53] objtool/klp: Rewrite symbol correlation algorithm

[Song Liu]

On Fri, May 1, 2026 at 5:09 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> Rewrite the symbol correlation code, using a tiered list of
> deterministic strategies in a loop.  For duplicately named symbols, each
> tier applies a filter with the goal of finding a 1:1 deterministic
> correlation between the original and patched version of the symbol.
>
> The three matching strategies are:
>
>   find_twin(): A funnel of progressively tighter filters.  Candidates
>   with the same demangled name are counted at four levels: name, scope
>   (local-vs-global), file (strict file association), and checksum
>   (unchanged functions).  The widest level that yields a 1:1 match wins,
>   narrower levels are only tried when the wider level is ambiguous.
>
>   find_twin_suffixed(): Uses already-correlated LLVM symbol pairs to map
>   .llvm.<hash> suffixes from orig to patched.  Because all promoted
>   symbols from the same TU share the same hash, one correlated pair
>   seeds the mapping for the entire TU.
>
>   find_twin_positional(): Last resort, matches symbols by position among
>   same-named candidates, similar to livepatch sympos.  Used for data
>   objects like __quirk variables where no deterministic filter can
>   distinguish the candidates.
>
> Overall this works much better than the existing algorithm, particularly
> with LTO kernels.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

Thanks for improving the correlation algorithm and adding detailed
comments about all these scenarios!

[PATCH v2 47/53] objtool/klp: Add correlation debugging output

[Josh Poimboeuf]

Add debugging messages to show how duplicate symbols get correlated, and
split the --debug feature into --debug-correlate and --debug-clone.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/include/objtool/warn.h | 16 +++++++----
 tools/objtool/klp-diff.c             | 42 ++++++++++++++++++++++------
 tools/objtool/objtool.c              |  3 --
 3 files changed, 45 insertions(+), 16 deletions(-)

diff --git a/tools/objtool/include/objtool/warn.h b/tools/objtool/include/objtool/warn.h
index 595ee8009667..a9936d60980c 100644
--- a/tools/objtool/include/objtool/warn.h
+++ b/tools/objtool/include/objtool/warn.h
@@ -109,7 +109,7 @@ static inline char *offstr(struct section *sec, unsigned long offset)
 #define ERROR_FUNC(sec, offset, format, ...) __WARN_FUNC(ERROR_STR, sec, offset, format, ##__VA_ARGS__)
 #define ERROR_INSN(insn, format, ...) ERROR_FUNC(insn->sec, insn->offset, format, ##__VA_ARGS__)
 
-extern bool debug;
+extern bool debug, debug_correlate, debug_clone;
 extern int indent;
 
 static inline void unindent(int *unused) { indent--; }
@@ -148,15 +148,21 @@ static inline void unindent(int *unused) { indent--; }
 		      (unsigned long long)checksum);			\
 })
 
-#define __dbg_indent(format, ...)					\
+#define dbg_correlate(args...)						\
 ({									\
-	if (unlikely(debug))						\
+	if (unlikely(debug_correlate))					\
+		__dbg(args);						\
+})
+
+#define __dbg_clone(format, ...)					\
+({									\
+	if (unlikely(debug_clone))					\
 		__dbg("%*s" format, indent * 8, "", ##__VA_ARGS__);	\
 })
 
-#define dbg_indent(args...)						\
+#define dbg_clone(args...)						\
 	int __cleanup(unindent) __dummy_##__COUNTER__;			\
-	__dbg_indent(args);						\
+	__dbg_clone(args);						\
 	indent++
 
 #endif /* _WARN_H */
diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index a9c993298b82..ed3bf1c55001 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -33,6 +33,9 @@ struct export {
 	char *mod, *sym;
 };
 
+bool debug, debug_correlate, debug_clone;
+int indent;
+
 static const char * const klp_diff_usage[] = {
 	"objtool klp diff [<options>] <in1.o> <in2.o> <out.o>",
 	NULL,
@@ -40,7 +43,9 @@ static const char * const klp_diff_usage[] = {
 
 static const struct option klp_diff_options[] = {
 	OPT_GROUP("Options:"),
-	OPT_BOOLEAN('d', "debug", &debug, "enable debug output"),
+	OPT_BOOLEAN('d', "debug", &debug, "enable all debug output"),
+	OPT_BOOLEAN(0, "debug-correlate", &debug_correlate, "enable correlation debug output"),
+	OPT_BOOLEAN(0, "debug-clone", &debug_clone, "enable cloning debug output"),
 	OPT_END(),
 };
 
@@ -583,6 +588,14 @@ static struct symbol *find_twin(struct elfs *e, struct symbol *sym1)
 	else if (csum_orig == 1 && csum_patched == 1)
 		match = csum_last;
 
+	if (!match)
+		return NULL;
+
+	if (name_orig != 1 || name_patched != 1)
+		dbg_correlate("find_twin(): %s%s -> %s%s",
+			      sym1->name, is_func_sym(sym1) ? "()" : "",
+			      match->name, is_func_sym(match) ? "()" : "");
+
 	return match;
 }
 
@@ -686,10 +699,14 @@ static struct symbol *find_twin_suffixed(struct elf *elf, struct symbol *sym1)
 		match = sym2;
 	}
 
-	if (count == 1)
-		return match;
+	if (count != 1)
+		return NULL;
 
-	return NULL;
+	dbg_correlate("find_suffixed_twin(): %s%s -> %s%s",
+		      sym1->name, is_func_sym(sym1) ? "()" : "",
+		      match->name, is_func_sym(match) ? "()" : "");
+
+	return match;
 }
 
 /*
@@ -742,6 +759,10 @@ static struct symbol *find_twin_positional(struct elfs *e, struct symbol *sym1)
 	if (idx_orig != idx_patched)
 		return NULL;
 
+	dbg_correlate("find_twin_positional(): %s%s -> %s%s",
+	    sym1->name, is_func_sym(sym1) ? "()" : "",
+	    match->name, is_func_sym(match) ? "()" : "");
+
 	return match;
 }
 
@@ -998,7 +1019,7 @@ static struct symbol *clone_symbol(struct elfs *e, struct symbol *patched_sym,
 	if (patched_sym->clone)
 		return patched_sym->clone;
 
-	dbg_indent("%s%s", patched_sym->name, data_too ? " [+DATA]" : "");
+	dbg_clone("%s%s", patched_sym->name, data_too ? " [+DATA]" : "");
 
 	/* Make sure the prefix gets cloned first */
 	if (is_func_sym(patched_sym) && data_too) {
@@ -1375,7 +1396,7 @@ static int clone_reloc_klp(struct elfs *e, struct reloc *patched_reloc,
 
 	klp_sym = find_symbol_by_name(e->out, sym_name);
 	if (!klp_sym) {
-		__dbg_indent("%s", sym_name);
+		__dbg_clone("%s", sym_name);
 
 		/* STB_WEAK: avoid modpost undefined symbol warnings */
 		klp_sym = elf_create_symbol(e->out, sym_name, NULL,
@@ -1426,7 +1447,7 @@ static int clone_reloc_klp(struct elfs *e, struct reloc *patched_reloc,
 }
 
 #define dbg_clone_reloc(sec, offset, patched_sym, addend, export, klp)			\
-	dbg_indent("%s+0x%lx: %s%s0x%lx [%s%s%s%s%s%s]",				\
+	dbg_clone("%s+0x%lx: %s%s0x%lx [%s%s%s%s%s%s]",					\
 		   sec->name, offset, patched_sym->name,				\
 		   addend >= 0 ? "+" : "-", labs(addend),				\
 		   sym_type(patched_sym),						\
@@ -1481,7 +1502,7 @@ static int clone_reloc(struct elfs *e, struct reloc *patched_reloc,
 	if (is_string_sec(patched_sym->sec)) {
 		const char *str = patched_sym->sec->data->d_buf + addend;
 
-		__dbg_indent("\"%s\"", escape_str(str));
+		__dbg_clone("\"%s\"", escape_str(str));
 
 		addend = elf_add_string(e->out, out_sym->sec, str);
 		if (addend == -1)
@@ -2121,6 +2142,11 @@ int cmd_klp_diff(int argc, const char **argv)
 	if (argc != 3)
 		usage_with_options(klp_diff_usage, klp_diff_options);
 
+	if (debug) {
+		debug_correlate = true;
+		debug_clone = true;
+	}
+
 	objname = argv[0];
 
 	e.orig = elf_open_read(argv[0], O_RDONLY);
diff --git a/tools/objtool/objtool.c b/tools/objtool/objtool.c
index 1c3622117c33..a4e139dee7e9 100644
--- a/tools/objtool/objtool.c
+++ b/tools/objtool/objtool.c
@@ -16,9 +16,6 @@
 #include <objtool/objtool.h>
 #include <objtool/warn.h>
 
-bool debug;
-int indent;
-
 static struct objtool_file file;
 
 struct objtool_file *objtool_open_read(const char *filename)
-- 
2.53.0

[PATCH v2 48/53] objtool: Add insn_sym() helper

[Josh Poimboeuf]

Alternative replacement instructions awkwardly have insn->sym set to the
function they get patched to rather than the symbol (or rather lack
thereof) they belong to in the file.

This makes it difficult to know where a given instruction actually
lives.

Add a new insn_sym() helper which preserves the existing semantic of
insn->sym.  Rename insn->sym to insn->_sym, which contains the actual
ELF binary symbol (or NULL, for alternative replacements) an instruction
lives in.

The private insn->_sym value will be needed for a subsequent patch.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/check.c                 | 31 ++++++++++++---------------
 tools/objtool/disas.c                 | 22 +++++++++----------
 tools/objtool/include/objtool/check.h | 20 +++++++++++++++--
 tools/objtool/include/objtool/warn.h  |  6 +++---
 tools/objtool/trace.c                 |  8 +++----
 5 files changed, 49 insertions(+), 38 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index ae047be919c5..410061aeed26 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -495,7 +495,7 @@ static int decode_instructions(struct objtool_file *file)
 			}
 
 			sym_for_each_insn(file, func, insn) {
-				insn->sym = func;
+				insn->_sym = func;
 				if (is_func_sym(func) &&
 				    insn->type == INSN_ENDBR &&
 				    list_empty(&insn->call_node)) {
@@ -859,15 +859,14 @@ static int create_ibt_endbr_seal_sections(struct objtool_file *file)
 	list_for_each_entry(insn, &file->endbr_list, call_node) {
 
 		int *site = (int *)sec->data->d_buf + idx;
-		struct symbol *sym = insn->sym;
+		struct symbol *func = insn_func(insn);
 		*site = 0;
 
-		if (opts.module && sym && is_func_sym(sym) &&
-		    insn->offset == sym->offset &&
-		    (!strcmp(sym->name, "init_module") ||
-		     !strcmp(sym->name, "cleanup_module"))) {
+		if (opts.module && func && insn->offset == func->offset &&
+		    (!strcmp(func->name, "init_module") ||
+		     !strcmp(func->name, "cleanup_module"))) {
 			ERROR("%s(): Magic init_module() function name is deprecated, use module_init(fn) instead",
-			      sym->name);
+			      func->name);
 			return -1;
 		}
 
@@ -1581,7 +1580,7 @@ static int add_jump_destinations(struct objtool_file *file)
 		}
 
 		if (!dest_sym || is_sec_sym(dest_sym)) {
-			dest_sym = dest_insn->sym;
+			dest_sym = insn_sym(dest_insn);
 			if (!dest_sym)
 				goto set_jump_dest;
 		}
@@ -1597,7 +1596,7 @@ static int add_jump_destinations(struct objtool_file *file)
 			continue;
 		}
 
-		if (!insn->sym || insn->sym->pfunc == dest_sym->pfunc)
+		if (!insn_sym(insn) || insn_sym(insn)->pfunc == dest_sym->pfunc)
 			goto set_jump_dest;
 
 		/*
@@ -1770,7 +1769,6 @@ static int handle_group_alt(struct objtool_file *file,
 		nop->offset = special_alt->new_off + special_alt->new_len;
 		nop->len = special_alt->orig_len - special_alt->new_len;
 		nop->type = INSN_NOP;
-		nop->sym = orig_insn->sym;
 		nop->alt_group = new_alt_group;
 		nop->fake = 1;
 	}
@@ -1789,7 +1787,6 @@ static int handle_group_alt(struct objtool_file *file,
 
 		last_new_insn = insn;
 
-		insn->sym = orig_insn->sym;
 		insn->alt_group = new_alt_group;
 
 		/*
@@ -2432,12 +2429,12 @@ static int __annotate_late(struct objtool_file *file, int type, struct instructi
 		break;
 
 	case ANNOTYPE_NOCFI:
-		sym = insn->sym;
+		sym = insn_sym(insn);
 		if (!sym) {
 			ERROR_INSN(insn, "dodgy NOCFI annotation");
 			return -1;
 		}
-		insn->sym->nocfi = 1;
+		insn_sym(insn)->nocfi = 1;
 		break;
 
 	default:
@@ -2538,7 +2535,7 @@ static void mark_holes(struct objtool_file *file)
 	 * favour of a regular symbol, but leaves the code in place.
 	 */
 	for_each_insn(file, insn) {
-		if (insn->sym || !find_symbol_hole_containing(insn->sec, insn->offset)) {
+		if (insn_sym(insn) || !find_symbol_hole_containing(insn->sec, insn->offset)) {
 			in_hole = false;
 			continue;
 		}
@@ -2982,7 +2979,7 @@ static int update_cfi_state(struct instruction *insn,
 			}
 
 			if (op->dest.reg == CFI_BP && op->src.reg == CFI_SP &&
-			    insn->sym->frame_pointer) {
+			    insn_sym(insn)->frame_pointer) {
 				/* addi.d fp,sp,imm on LoongArch */
 				if (cfa->base == CFI_SP && cfa->offset == op->src.offset) {
 					cfa->base = CFI_BP;
@@ -2994,7 +2991,7 @@ static int update_cfi_state(struct instruction *insn,
 			if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
 				/* addi.d sp,fp,imm on LoongArch */
 				if (cfa->base == CFI_BP && cfa->offset == 0) {
-					if (insn->sym->frame_pointer) {
+					if (insn_sym(insn)->frame_pointer) {
 						cfa->base = CFI_SP;
 						cfa->offset = -op->src.offset;
 					}
@@ -4171,7 +4168,7 @@ static int validate_retpoline(struct objtool_file *file)
 	 * broken.
 	 */
 	list_for_each_entry(insn, &file->retpoline_call_list, call_node) {
-		struct symbol *sym = insn->sym;
+		struct symbol *sym = insn_sym(insn);
 
 		if (sym && (is_notype_sym(sym) ||
 			    is_func_sym(sym)) && !sym->nocfi) {
diff --git a/tools/objtool/disas.c b/tools/objtool/disas.c
index 59090234af19..e6a54a83605c 100644
--- a/tools/objtool/disas.c
+++ b/tools/objtool/disas.c
@@ -210,7 +210,7 @@ static bool disas_print_addr_alt(bfd_vma addr, struct disassemble_info *dinfo)
 	offset = addr - alt_group->first_insn->offset;
 
 	addr = orig_first_insn->offset + offset;
-	sym = orig_first_insn->sym;
+	sym = insn_sym(orig_first_insn);
 
 	disas_print_addr_sym(orig_first_insn->sec, sym, addr, dinfo);
 
@@ -222,15 +222,13 @@ static void disas_print_addr_noreloc(bfd_vma addr,
 {
 	struct disas_context *dctx = dinfo->application_data;
 	struct instruction *insn = dctx->insn;
-	struct symbol *sym = NULL;
+	struct symbol *sym = insn_sym(insn);
 
 	if (disas_print_addr_alt(addr, dinfo))
 		return;
 
-	if (insn->sym && addr >= insn->sym->offset &&
-	    addr < insn->sym->offset + insn->sym->len) {
-		sym = insn->sym;
-	}
+	if (sym && (addr < sym->offset || addr >= sym->offset + sym->len))
+		sym = NULL;
 
 	disas_print_addr_sym(insn->sec, sym, addr, dinfo);
 }
@@ -291,9 +289,9 @@ static void disas_print_address(bfd_vma addr, struct disassemble_info *dinfo)
 	 * up. So check it first.
 	 */
 	jump_dest = insn->jump_dest;
-	if (jump_dest && jump_dest->sym && jump_dest->offset == addr) {
+	if (jump_dest && insn_sym(jump_dest) && jump_dest->offset == addr) {
 		if (!disas_print_addr_alt(addr, dinfo))
-			disas_print_addr_sym(jump_dest->sec, jump_dest->sym,
+			disas_print_addr_sym(jump_dest->sec, insn_sym(jump_dest),
 					     addr, dinfo);
 		return;
 	}
@@ -768,8 +766,8 @@ static int disas_alt_jump(struct disas_alt *dalt)
 		if (orig_insn->len == 5)
 			suffix[0] = 'q';
 		str = strfmt("jmp%-3s %lx <%s+0x%lx>", suffix,
-			     dest_insn->offset, dest_insn->sym->name,
-			     dest_insn->offset - dest_insn->sym->offset);
+			     dest_insn->offset, insn_sym(dest_insn)->name,
+			     dest_insn->offset - insn_sym(dest_insn)->offset);
 		nops = 0;
 	} else {
 		str = strfmt("nop%d", orig_insn->len);
@@ -794,8 +792,8 @@ static int disas_alt_extable(struct disas_alt *dalt)
 
 	alt_insn = dalt->alt->insn;
 	str = strfmt("resume at 0x%lx <%s+0x%lx>",
-		     alt_insn->offset, alt_insn->sym->name,
-		     alt_insn->offset - alt_insn->sym->offset);
+		     alt_insn->offset, insn_sym(alt_insn)->name,
+		     alt_insn->offset - insn_sym(alt_insn)->offset);
 	if (!str)
 		return -1;
 
diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h
index eea64728d39b..fe08205d8eb1 100644
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@@ -94,14 +94,30 @@ struct instruction {
 		};
 	};
 	struct alternative *alts;
-	struct symbol *sym;
+	struct symbol *_sym;
 	struct stack_op *stack_ops;
 	struct cfi_state *cfi;
 };
 
+/*
+ * Return the symbol associated with an instruction.  For alternative
+ * replacements, return the symbol of the original code being replaced rather
+ * than NULL.  insn->_sym reflects the actual location in the ELF file.
+ */
+static inline struct symbol *insn_sym(struct instruction *insn)
+{
+	struct symbol *sym = insn->_sym;
+
+	if ((!sym || !is_func_sym(sym)) &&
+	    insn->alt_group && insn->alt_group->orig_group)
+		sym = insn->alt_group->orig_group->first_insn->_sym;
+
+	return sym;
+}
+
 static inline struct symbol *insn_func(struct instruction *insn)
 {
-	struct symbol *sym = insn->sym;
+	struct symbol *sym = insn_sym(insn);
 
 	if (sym && sym->type != STT_FUNC)
 		sym = NULL;
diff --git a/tools/objtool/include/objtool/warn.h b/tools/objtool/include/objtool/warn.h
index a9936d60980c..870e147f3a56 100644
--- a/tools/objtool/include/objtool/warn.h
+++ b/tools/objtool/include/objtool/warn.h
@@ -77,13 +77,13 @@ static inline char *offstr(struct section *sec, unsigned long offset)
 #define WARN_INSN(insn, format, ...)					\
 ({									\
 	struct instruction *_insn = (insn);				\
-	if (!_insn->sym || !_insn->sym->warned)	{			\
+	if (!insn_sym(_insn) || !insn_sym(_insn)->warned)	{	\
 		WARN_FUNC(_insn->sec, _insn->offset, format,		\
 			  ##__VA_ARGS__);				\
 		BT_INSN(_insn, "");					\
 	}								\
-	if (_insn->sym)							\
-		_insn->sym->warned = 1;					\
+	if (insn_sym(_insn))						\
+		insn_sym(_insn)->warned = 1;				\
 })
 
 #define BT_INSN(insn, format, ...)				\
diff --git a/tools/objtool/trace.c b/tools/objtool/trace.c
index 5dec44dab781..61c6aa302bc3 100644
--- a/tools/objtool/trace.c
+++ b/tools/objtool/trace.c
@@ -169,8 +169,8 @@ void trace_alt_begin(struct instruction *orig_insn, struct alternative *alt,
 		 */
 		TRACE_ALT_INFO_NOADDR(orig_insn, "/ ", "%s for instruction at 0x%lx <%s+0x%lx>",
 				      alt_name,
-				      orig_insn->offset, orig_insn->sym->name,
-				      orig_insn->offset - orig_insn->sym->offset);
+				      orig_insn->offset, insn_sym(orig_insn)->name,
+				      orig_insn->offset - insn_sym(orig_insn)->offset);
 	} else {
 		TRACE_ALT_INFO_NOADDR(orig_insn, "/ ", "%s", alt_name);
 	}
@@ -185,8 +185,8 @@ void trace_alt_begin(struct instruction *orig_insn, struct alternative *alt,
 		if (orig_insn->type == INSN_NOP) {
 			suffix[0] = (orig_insn->len == 5) ? 'q' : '\0';
 			TRACE_ADDR(orig_insn, "jmp%-3s %lx <%s+0x%lx>", suffix,
-				   alt_insn->offset, alt_insn->sym->name,
-				   alt_insn->offset - alt_insn->sym->offset);
+				   alt_insn->offset, insn_sym(alt_insn)->name,
+				   alt_insn->offset - insn_sym(alt_insn)->offset);
 		} else {
 			TRACE_ADDR(orig_insn, "nop%d", orig_insn->len);
 			trace_depth--;
-- 
2.53.0

Re: [PATCH v2 48/53] objtool: Add insn_sym() helper

[Song Liu]

On Fri, May 1, 2026 at 5:09 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> Alternative replacement instructions awkwardly have insn->sym set to the
> function they get patched to rather than the symbol (or rather lack
> thereof) they belong to in the file.
>
> This makes it difficult to know where a given instruction actually
> lives.
>
> Add a new insn_sym() helper which preserves the existing semantic of
> insn->sym.  Rename insn->sym to insn->_sym, which contains the actual
> ELF binary symbol (or NULL, for alternative replacements) an instruction
> lives in.
>
> The private insn->_sym value will be needed for a subsequent patch.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

[PATCH v2 49/53] objtool/klp: Fix position-dependent checksums for non-relocated jumps/calls

[Josh Poimboeuf]

When computing klp checksums, instructions with non-relocated jump/call
destination offsets are problematic because the offset values can change
when surrounding code has moved, causing the function to be incorrectly
marked as changed.

Specifically, that includes jumps from alternatives to the end of the
alternative, which from objtool's perspective are jumps to the end of
the alternative instruction block in the original function.

Note that 'jump_dest' jumps don't include sibling calls (those use
call_dest), nor do they include jumps to/from .cold sub functions (those
are cross-section and need a reloc).

Fix it by hashing the opcode bytes (excluding the immediate operand)
along with a position-independent representation of the destination.
For calls, use the function name, and for jumps, use the destination's
offset within its function.

[Note the "9 bit hole" comment was wrong: it has been 8 bits since
commit 70589843b36f ("objtool: Add option to trace function validation")
added the 'trace' field.  Adding the 4-bit 'immediate_len' field now
leaves a 4-bit hole.]

Fixes: 0d83da43b1e1 ("objtool/klp: Add --checksum option to generate per-function checksums")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/arch/x86/decode.c       | 17 ++++++++-
 tools/objtool/include/objtool/arch.h  |  3 ++
 tools/objtool/include/objtool/check.h |  3 +-
 tools/objtool/klp-checksum.c          | 53 ++++++++++++++++++++++++---
 4 files changed, 67 insertions(+), 9 deletions(-)

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 350b8ee6e776..1b387d5a195b 100644
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -805,14 +805,27 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
 		break;
 	}
 
-	if (ins.immediate.nbytes)
+	if (ins.immediate.nbytes) {
 		insn->immediate = ins.immediate.value;
-	else if (ins.displacement.nbytes)
+		insn->immediate_len = ins.immediate.nbytes;
+	} else if (ins.displacement.nbytes) {
 		insn->immediate = ins.displacement.value;
+		insn->immediate_len = ins.displacement.nbytes;
+	}
 
 	return 0;
 }
 
+size_t arch_jump_opcode_bytes(struct objtool_file *file, struct instruction *insn,
+			      unsigned char *buf)
+{
+	size_t len;
+
+	len = insn->len - insn->immediate_len;
+	memcpy(buf, insn->sec->data->d_buf + insn->offset, len);
+	return len;
+}
+
 void arch_initial_func_cfi_state(struct cfi_init_state *state)
 {
 	int i;
diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
index 8866158975fc..96d828a8401f 100644
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -79,6 +79,9 @@ int arch_decode_instruction(struct objtool_file *file, const struct section *sec
 			    unsigned long offset, unsigned int maxlen,
 			    struct instruction *insn);
 
+size_t arch_jump_opcode_bytes(struct objtool_file *file, struct instruction *insn,
+			      unsigned char *buf);
+
 bool arch_callee_saved_reg(unsigned char reg);
 
 unsigned long arch_jump_destination(struct instruction *insn);
diff --git a/tools/objtool/include/objtool/check.h b/tools/objtool/include/objtool/check.h
index fe08205d8eb1..063f5985fecd 100644
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@@ -68,6 +68,7 @@ struct instruction {
 	s8 instr;
 
 	u32 idx			: INSN_CHUNK_BITS,
+	    immediate_len	: 4,
 	    dead_end		: 1,
 	    ignore_alts		: 1,
 	    hint		: 1,
@@ -81,7 +82,7 @@ struct instruction {
 	    hole		: 1,
 	    fake		: 1,
 	    trace		: 1;
-		/* 9 bit hole */
+		/* 4 bit hole */
 
 	struct alt_group *alt_group;
 	struct instruction *jump_dest;
diff --git a/tools/objtool/klp-checksum.c b/tools/objtool/klp-checksum.c
index 19653dbe109d..b8e47f28997e 100644
--- a/tools/objtool/klp-checksum.c
+++ b/tools/objtool/klp-checksum.c
@@ -66,17 +66,58 @@ static void checksum_update_insn(struct objtool_file *file, struct symbol *func,
 	if (insn->fake)
 		return;
 
-	__checksum_update_insn(func, insn, insn->sec->data->d_buf + insn->offset, insn->len);
-
 	if (!reloc) {
 		struct symbol *call_dest = insn_call_dest(insn);
+		struct instruction *jump_dest = insn->jump_dest;
 
-		if (call_dest)
-			__checksum_update_insn(func, insn, call_dest->demangled_name,
-					       strlen(call_dest->demangled_name));
-		goto alts;
+		/*
+		 * For a jump/call non-relocated dest offset embedded in the
+		 * instruction, the offset may vary due to changes in
+		 * surrounding code.  Just hash the opcode and a
+		 * position-independent representation of the destination.
+		 */
+
+		if (call_dest || jump_dest) {
+			unsigned char buf[16];
+			size_t len;
+
+			len = arch_jump_opcode_bytes(file, insn, buf);
+			__checksum_update_insn(func, insn, buf, len);
+
+			if (call_dest) {
+				__checksum_update_insn(func, insn, call_dest->demangled_name,
+						       strlen(call_dest->demangled_name));
+
+			} else if (jump_dest) {
+				struct symbol *dest_sym;
+				unsigned long offset;
+
+				/*
+				 * use insn->_sym instead of insn_sym() here.
+				 * For alternative replacements, the latter
+				 * would give the function of the code being
+				 * replaced.
+				 */
+				dest_sym = jump_dest->_sym;
+				if (!dest_sym)
+					goto alts;
+
+				__checksum_update_insn(func, insn, dest_sym->demangled_name,
+						       strlen(dest_sym->demangled_name));
+
+				offset = jump_dest->offset - dest_sym->offset;
+				__checksum_update_insn(func, insn, &offset, sizeof(offset));
+			}
+
+			goto alts;
+		}
 	}
 
+	__checksum_update_insn(func, insn, insn->sec->data->d_buf + insn->offset, insn->len);
+
+	if (!reloc)
+		goto alts;
+
 	sym = reloc->sym;
 	offset = arch_insn_adjusted_addend(insn, reloc);
 
-- 
2.53.0

Re: [PATCH v2 49/53] objtool/klp: Fix position-dependent checksums for non-relocated jumps/calls

[Song Liu]

On Fri, May 1, 2026 at 5:09 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> When computing klp checksums, instructions with non-relocated jump/call
> destination offsets are problematic because the offset values can change
> when surrounding code has moved, causing the function to be incorrectly
> marked as changed.
>
> Specifically, that includes jumps from alternatives to the end of the
> alternative, which from objtool's perspective are jumps to the end of
> the alternative instruction block in the original function.
>
> Note that 'jump_dest' jumps don't include sibling calls (those use
> call_dest), nor do they include jumps to/from .cold sub functions (those
> are cross-section and need a reloc).
>
> Fix it by hashing the opcode bytes (excluding the immediate operand)
> along with a position-independent representation of the destination.
> For calls, use the function name, and for jumps, use the destination's
> offset within its function.
>
> [Note the "9 bit hole" comment was wrong: it has been 8 bits since
> commit 70589843b36f ("objtool: Add option to trace function validation")
> added the 'trace' field.  Adding the 4-bit 'immediate_len' field now
> leaves a 4-bit hole.]
>
> Fixes: 0d83da43b1e1 ("objtool/klp: Add --checksum option to generate per-function checksums")
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

[PATCH v2 50/53] objtool: Grow __cfi_* prefix symbols for all CFI+CALL_PADDING

[Josh Poimboeuf]

For all CONFIG_CFI+CONFIG_CALL_PADDING configs, for C functions, the
__cfi_ symbols only cover the 5-byte kCFI type hash.  After that there
also N bytes of NOP padding between the hash and the function entry
which aren't associated with any symbol.

The NOPs can be replaced with actual code at runtime.  Without a symbol,
unwinders and tooling have no way of knowing where those bytes belong.

Grow the existing __cfi_* symbols to fill that gap.

Note that assembly functions with SYM_TYPED_FUNC_START() aren't affected
by this issue, their __cfi_ symbols also cover the padding.

Also, CONFIG_PREFIX_SYMBOLS has no reason to exist: CONFIG_CALL_PADDING
is what causes the compiler to emit NOP padding before function entry
(via -fpatchable-function-entry), so it's the right condition for
creating prefix symbols.

Remove CONFIG_PREFIX_SYMBOLS, as it's no longer needed.  Simplify the
LONGEST_SYM_KUNIT_TEST dependency accordingly.  Rework objtool's
arguments a bit to handle the variety of prefix/cfi-related cases.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 arch/x86/Kconfig                        |  4 --
 lib/Kconfig.debug                       |  2 +-
 scripts/Makefile.lib                    |  7 +++-
 tools/objtool/builtin-check.c           | 15 +++++++-
 tools/objtool/check.c                   | 49 ++++++++++++++++++++-----
 tools/objtool/elf.c                     | 20 ++++++++++
 tools/objtool/include/objtool/builtin.h |  7 ++--
 tools/objtool/include/objtool/elf.h     |  1 +
 8 files changed, 84 insertions(+), 21 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f3f7cb01d69d..3eb3c48d764a 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2437,10 +2437,6 @@ config CALL_THUNKS
 	def_bool n
 	select CALL_PADDING
 
-config PREFIX_SYMBOLS
-	def_bool y
-	depends on CALL_PADDING && !CFI
-
 menuconfig CPU_MITIGATIONS
 	bool "Mitigations for CPU vulnerabilities"
 	default y
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 8ff5adcfe1e0..4f7496b3268d 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -3070,7 +3070,7 @@ config FORTIFY_KUNIT_TEST
 config LONGEST_SYM_KUNIT_TEST
 	tristate "Test the longest symbol possible" if !KUNIT_ALL_TESTS
 	depends on KUNIT && KPROBES
-	depends on !PREFIX_SYMBOLS && !CFI && !GCOV_KERNEL
+	depends on !CALL_PADDING && !CFI && !GCOV_KERNEL
 	default KUNIT_ALL_TESTS
 	help
 	  Tests the longest symbol possible
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 0718e39cedda..7e216d82e988 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -187,7 +187,11 @@ objtool-args-$(CONFIG_HAVE_JUMP_LABEL_HACK)		+= --hacks=jump_label
 objtool-args-$(CONFIG_HAVE_NOINSTR_HACK)		+= --hacks=noinstr
 objtool-args-$(CONFIG_MITIGATION_CALL_DEPTH_TRACKING)	+= --hacks=skylake
 objtool-args-$(CONFIG_X86_KERNEL_IBT)			+= --ibt
-objtool-args-$(CONFIG_FINEIBT)				+= --cfi
+objtool-args-$(CONFIG_CALL_PADDING)			+= --prefix=$(CONFIG_FUNCTION_PADDING_BYTES)
+ifdef CONFIG_CALL_PADDING
+objtool-args-$(CONFIG_CFI)				+= --cfi
+objtool-args-$(CONFIG_FINEIBT)				+= --fineibt
+endif
 objtool-args-$(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL)	+= --mcount
 ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
 objtool-args-$(CONFIG_HAVE_OBJTOOL_NOP_MCOUNT)		+= --mnop
@@ -200,7 +204,6 @@ objtool-args-$(CONFIG_STACK_VALIDATION)			+= --stackval
 objtool-args-$(CONFIG_HAVE_STATIC_CALL_INLINE)		+= --static-call
 objtool-args-$(CONFIG_HAVE_UACCESS_VALIDATION)		+= --uaccess
 objtool-args-$(or $(CONFIG_GCOV_KERNEL),$(CONFIG_KCOV))	+= --no-unreachable
-objtool-args-$(CONFIG_PREFIX_SYMBOLS)			+= --prefix=$(CONFIG_FUNCTION_PADDING_BYTES)
 objtool-args-$(CONFIG_OBJTOOL_WERROR)			+= --werror
 
 objtool-args = $(objtool-args-y)					\
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index ec7f10a5ef19..118c3de2f293 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -73,7 +73,6 @@ static int parse_hacks(const struct option *opt, const char *str, int unset)
 
 static const struct option check_options[] = {
 	OPT_GROUP("Actions:"),
-	OPT_BOOLEAN(0,		 "cfi", &opts.cfi, "annotate kernel control flow integrity (kCFI) function preambles"),
 	OPT_STRING_OPTARG('d',	 "disas", &opts.disas, "function-pattern", "disassemble functions", "*"),
 	OPT_CALLBACK_OPTARG('h', "hacks", NULL, NULL, "jump_label,noinstr,skylake", "patch toolchain bugs/limitations", parse_hacks),
 	OPT_BOOLEAN('i',	 "ibt", &opts.ibt, "validate and annotate IBT"),
@@ -84,7 +83,7 @@ static const struct option check_options[] = {
 	OPT_BOOLEAN('r',	 "retpoline", &opts.retpoline, "validate and annotate retpoline usage"),
 	OPT_BOOLEAN(0,		 "rethunk", &opts.rethunk, "validate and annotate rethunk usage"),
 	OPT_BOOLEAN(0,		 "unret", &opts.unret, "validate entry unret placement"),
-	OPT_INTEGER(0,		 "prefix", &opts.prefix, "generate prefix symbols"),
+	OPT_INTEGER(0,		 "prefix", &opts.prefix, "generate or grow prefix symbols for N-byte function padding"),
 	OPT_BOOLEAN('l',	 "sls", &opts.sls, "validate straight-line-speculation mitigations"),
 	OPT_BOOLEAN('s',	 "stackval", &opts.stackval, "validate frame pointer rules"),
 	OPT_BOOLEAN('t',	 "static-call", &opts.static_call, "annotate static calls"),
@@ -92,6 +91,8 @@ static const struct option check_options[] = {
 	OPT_CALLBACK_OPTARG(0,	 "dump", NULL, NULL, "orc", "dump metadata", parse_dump),
 
 	OPT_GROUP("Options:"),
+	OPT_BOOLEAN(0,		 "cfi", &opts.cfi, "grow kCFI preamble symbols (use with --prefix)"),
+	OPT_BOOLEAN(0,		 "fineibt", &opts.fineibt, "create .cfi_sites section for FineIBT"),
 	OPT_BOOLEAN(0,		 "backtrace", &opts.backtrace, "unwind on error"),
 	OPT_BOOLEAN(0,		 "backup", &opts.backup, "create backup (.orig) file on warning/error"),
 	OPT_BOOLEAN(0,		 "dry-run", &opts.dryrun, "don't write modifications"),
@@ -163,6 +164,16 @@ static bool opts_valid(void)
 		return false;
 	}
 
+	if (opts.cfi && !opts.prefix) {
+		ERROR("--cfi requires --prefix");
+		return false;
+	}
+
+	if (opts.fineibt && !opts.cfi) {
+		ERROR("--fineibt requires --cfi");
+		return false;
+	}
+
 	if (opts.disas			||
 	    opts.hack_jump_label	||
 	    opts.hack_noinstr		||
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 410061aeed26..0d9b859b006e 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -881,6 +881,31 @@ static int create_ibt_endbr_seal_sections(struct objtool_file *file)
 	return 0;
 }
 
+/*
+* Grow __cfi_ symbols to fill the NOP gap between the 'mov <hash>, %rax' and
+* the start of the function.
+*/
+static int grow_cfi_symbols(struct objtool_file *file)
+{
+	struct symbol *sym;
+
+	for_each_sym(file->elf, sym) {
+		if (!is_func_sym(sym) || !strstarts(sym->name, "__cfi_") ||
+		    sym->len != 5)
+			continue;
+
+		if (!find_func_by_offset(sym->sec, sym->offset + sym->len + opts.prefix))
+			continue;
+
+		sym->len += opts.prefix;
+		sym->sym.st_size = sym->len;
+		if (elf_write_symbol(file->elf, sym))
+			return -1;
+	}
+
+	return 0;
+}
+
 static int create_cfi_sections(struct objtool_file *file)
 {
 	struct section *sec;
@@ -4903,12 +4928,6 @@ int check(struct objtool_file *file)
 			goto out;
 	}
 
-	if (opts.cfi) {
-		ret = create_cfi_sections(file);
-		if (ret)
-			goto out;
-	}
-
 	if (opts.rethunk) {
 		ret = create_return_sites_sections(file);
 		if (ret)
@@ -4928,9 +4947,21 @@ int check(struct objtool_file *file)
 	}
 
 	if (opts.prefix) {
-		ret = create_prefix_symbols(file);
-		if (ret)
-			goto out;
+		if (!opts.cfi) {
+			ret = create_prefix_symbols(file);
+			if (ret)
+				goto out;
+		} else {
+			ret = grow_cfi_symbols(file);
+			if (ret)
+				goto out;
+
+			if (opts.fineibt) {
+				ret = create_cfi_sections(file);
+				if (ret)
+					goto out;
+			}
+		}
 	}
 
 	if (opts.ibt) {
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index d9cee8d5d9e8..33c95a74a51b 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -997,6 +997,26 @@ struct symbol *elf_create_symbol(struct elf *elf, const char *name,
 	return sym;
 }
 
+int elf_write_symbol(struct elf *elf, struct symbol *sym)
+{
+	struct section *symtab, *symtab_shndx;
+
+	symtab = find_section_by_name(elf, ".symtab");
+	if (!symtab) {
+		ERROR("no .symtab");
+		return -1;
+	}
+
+	symtab_shndx = find_section_by_name(elf, ".symtab_shndx");
+
+	if (elf_update_symbol(elf, symtab, symtab_shndx, sym))
+		return -1;
+
+	mark_sec_changed(elf, symtab, true);
+
+	return 0;
+}
+
 struct symbol *elf_create_section_symbol(struct elf *elf, struct section *sec)
 {
 	struct symbol *sym = calloc(1, sizeof(*sym));
diff --git a/tools/objtool/include/objtool/builtin.h b/tools/objtool/include/objtool/builtin.h
index b9e229ed4dc0..e844e9c82b7b 100644
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -9,8 +9,8 @@
 
 struct opts {
 	/* actions: */
-	bool cfi;
 	bool checksum;
+	const char *disas;
 	bool dump_orc;
 	bool hack_jump_label;
 	bool hack_noinstr;
@@ -20,6 +20,7 @@ struct opts {
 	bool noabs;
 	bool noinstr;
 	bool orc;
+	int prefix;
 	bool retpoline;
 	bool rethunk;
 	bool unret;
@@ -27,14 +28,14 @@ struct opts {
 	bool stackval;
 	bool static_call;
 	bool uaccess;
-	int prefix;
-	const char *disas;
 
 	/* options: */
 	bool backtrace;
 	bool backup;
+	bool cfi;
 	const char *debug_checksum;
 	bool dryrun;
+	bool fineibt;
 	bool link;
 	bool mnop;
 	bool module;
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index e452784df702..305183f30a33 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -199,6 +199,7 @@ struct reloc *elf_init_reloc_data_sym(struct elf *elf, struct section *sec,
 				      struct symbol *sym,
 				      s64 addend);
 
+int elf_write_symbol(struct elf *elf, struct symbol *sym);
 int elf_write_insn(struct elf *elf, struct section *sec, unsigned long offset,
 		   unsigned int len, const char *insn);
 
-- 
2.53.0

[PATCH v2 51/53] objtool/klp: Fix kCFI prefix finding/cloning

[Josh Poimboeuf]

With CFI+CALL_PADDING, Clang places .Ltmp labels at the start of the NOP
padding (offset 5) between the __cfi_ prefix and the function entry
point.  get_func_prefix() only checks the immediately previous symbol,
so the intervening .Ltmp label causes it to miss the __cfi_ prefix
symbol.

This results in klp-diff not cloning the kCFI type hash into the
livepatch module, causing a CFI failure at module load when calling
callback functions through indirect calls:

  CFI failure at __klp_enable_patch+0xab/0x140
    (target: pre_patch_callback+0x0/0x80 [livepatch_combined];
     expected type: 0xde073954)

Instead of walking backward through the section's symbol list, just use
find_func_containing() for the byte before the function.  This works now
that __cfi_ symbols are being grown by objtool to fill the padding.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/include/objtool/elf.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index 305183f30a33..fccf72cbd343 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -539,10 +539,10 @@ static inline struct symbol *get_func_prefix(struct symbol *func)
 {
 	struct symbol *prev;
 
-	if (!is_func_sym(func))
+	if (!is_func_sym(func) || !func->offset)
 		return NULL;
 
-	prev = sec_prev_sym(func);
+	prev = find_func_containing(func->sec, func->offset - 1);
 	if (prev && is_prefix_func(prev))
 		return prev;
 
-- 
2.53.0

Re: [PATCH v2 51/53] objtool/klp: Fix kCFI prefix finding/cloning

[Song Liu]

On Fri, May 1, 2026 at 5:09 AM Josh Poimboeuf <jpoimboe@kernel.org> wrote:
>
> With CFI+CALL_PADDING, Clang places .Ltmp labels at the start of the NOP
> padding (offset 5) between the __cfi_ prefix and the function entry
> point.  get_func_prefix() only checks the immediately previous symbol,
> so the intervening .Ltmp label causes it to miss the __cfi_ prefix
> symbol.
>
> This results in klp-diff not cloning the kCFI type hash into the
> livepatch module, causing a CFI failure at module load when calling
> callback functions through indirect calls:
>
>   CFI failure at __klp_enable_patch+0xab/0x140
>     (target: pre_patch_callback+0x0/0x80 [livepatch_combined];
>      expected type: 0xde073954)
>
> Instead of walking backward through the section's symbol list, just use
> find_func_containing() for the byte before the function.  This works now
> that __cfi_ symbols are being grown by objtool to fill the padding.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Acked-by: Song Liu <song@kernel.org>

[PATCH v2 52/53] objtool: Improve and simplify prefix symbol detection

[Josh Poimboeuf]

Only create prefix symbols for functions that have
__patchable_function_entries entries, since those are the only C
functions where prefix NOPs are intentional.

This both simplifies the detection and makes it more accurate.

Note that assembly functions using SYM_TYPED_FUNC_START() can also have
prefixed NOPs, but that macro already creates their __cfi_ symbols.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/check.c | 90 ++++++++++---------------------------------
 1 file changed, 21 insertions(+), 69 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 0d9b859b006e..1635c87a4ac8 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4296,17 +4296,6 @@ static bool ignore_unreachable_insn(struct objtool_file *file, struct instructio
  * For FineIBT or kCFI, a certain number of bytes preceding the function may be
  * NOPs.  Those NOPs may be rewritten at runtime and executed, so give them a
  * proper function name: __pfx_<func>.
- *
- * The NOPs may not exist for the following cases:
- *
- *   - compiler cloned functions (*.cold, *.part0, etc)
- *   - asm functions created with inline asm or without SYM_FUNC_START()
- *
- * Also, the function may already have a prefix from a previous objtool run
- * (livepatch extracted functions, or manually running objtool multiple times).
- *
- * So return 0 if the NOPs are missing or the function already has a prefix
- * symbol.
  */
 static int create_prefix_symbol(struct objtool_file *file, struct symbol *func)
 {
@@ -4314,10 +4303,6 @@ static int create_prefix_symbol(struct objtool_file *file, struct symbol *func)
 	char name[SYM_NAME_LEN];
 	struct cfi_state *cfi;
 
-	if (!is_func_sym(func) || is_prefix_func(func) || is_cold_func(func) ||
-	    func->static_call_tramp)
-		return 0;
-
 	if ((strlen(func->name) + sizeof("__pfx_") > SYM_NAME_LEN)) {
 		WARN("%s: symbol name too long, can't create __pfx_ symbol",
 		      func->name);
@@ -4327,59 +4312,21 @@ static int create_prefix_symbol(struct objtool_file *file, struct symbol *func)
 	if (snprintf_check(name, SYM_NAME_LEN, "__pfx_%s", func->name))
 		return -1;
 
-	if (file->klp) {
-		struct symbol *pfx;
-
-		pfx = find_symbol_by_offset(func->sec, func->offset - opts.prefix);
-		if (pfx && is_prefix_func(pfx) && !strcmp(pfx->name, name))
-			return 0;
-	}
-
-	insn = find_insn(file, func->sec, func->offset);
-	if (!insn) {
-		WARN("%s: can't find starting instruction", func->name);
+	if (!elf_create_symbol(file->elf, name, func->sec,
+			       GELF_ST_BIND(func->sym.st_info),
+			       GELF_ST_TYPE(func->sym.st_info),
+			       func->offset - opts.prefix, opts.prefix))
 		return -1;
-	}
-
-	for (prev = prev_insn_same_sec(file, insn);
-	     prev;
-	     prev = prev_insn_same_sec(file, prev)) {
-		u64 offset;
-
-		if (prev->type != INSN_NOP)
-			return 0;
-
-		offset = func->offset - prev->offset;
-
-		if (offset > opts.prefix)
-			return 0;
-
-		if (offset < opts.prefix)
-			continue;
-
-		if (!elf_create_symbol(file->elf, name, func->sec,
-				       GELF_ST_BIND(func->sym.st_info),
-				       GELF_ST_TYPE(func->sym.st_info),
-				       prev->offset, opts.prefix))
-			return -1;
-
-		break;
-	}
-
-	if (!prev)
-		return 0;
-
-	if (!insn->cfi) {
-		/*
-		 * This can happen if stack validation isn't enabled or the
-		 * function is annotated with STACK_FRAME_NON_STANDARD.
-		 */
-		return 0;
-	}
 
 	/* Propagate insn->cfi to the prefix code */
+	insn = find_insn(file, func->sec, func->offset);
+	if (!insn || !insn->cfi)
+		return 0;
+
 	cfi = cfi_hash_find_or_add(insn->cfi);
-	for (; prev != insn; prev = next_insn_same_sec(file, prev))
+	for (prev = find_insn(file, func->sec, func->offset - opts.prefix);
+	     prev && prev != insn;
+	     prev = next_insn_same_sec(file, prev))
 		prev->cfi = cfi;
 
 	return 0;
@@ -4387,15 +4334,20 @@ static int create_prefix_symbol(struct objtool_file *file, struct symbol *func)
 
 static int create_prefix_symbols(struct objtool_file *file)
 {
-	struct section *sec;
+	struct section *pfe_sec;
 	struct symbol *func;
+	struct reloc *reloc;
 
-	for_each_sec(file->elf, sec) {
-		if (!is_text_sec(sec))
+	for_each_sec(file->elf, pfe_sec) {
+		if (strcmp(pfe_sec->name, "__patchable_function_entries"))
+			continue;
+		if (!pfe_sec->rsec)
 			continue;
 
-		sec_for_each_sym(sec, func) {
-			if (create_prefix_symbol(file, func))
+		for_each_reloc(pfe_sec->rsec, reloc) {
+			func = find_func_by_offset(reloc->sym->sec,
+						   reloc->sym->offset + reloc_addend(reloc) + opts.prefix);
+			if (func && create_prefix_symbol(file, func))
 				return -1;
 		}
 	}
-- 
2.53.0

[PATCH v2 53/53] objtool/klp: Cache dont_correlate() result

[Josh Poimboeuf]

Cache the dont_correlate() result once per symbol at the start of
correlate_symbols().  This reduces klp diff time on an arm64 LTO
vmlinux.o from 2m51s to 35s.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
 tools/objtool/include/objtool/elf.h |  1 +
 tools/objtool/klp-diff.c            | 29 +++++++++++++++++------------
 2 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index fccf72cbd343..d9c44df9cc76 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -96,6 +96,7 @@ struct symbol {
 	u8 changed	     : 1;
 	u8 included	     : 1;
 	u8 klp		     : 1;
+	u8 dont_correlate    : 1;
 	struct list_head pv_target;
 	struct reloc *relocs;
 	struct section *group_sec;
diff --git a/tools/objtool/klp-diff.c b/tools/objtool/klp-diff.c
index ed3bf1c55001..f8787d7d1454 100644
--- a/tools/objtool/klp-diff.c
+++ b/tools/objtool/klp-diff.c
@@ -524,7 +524,7 @@ static struct symbol *find_twin(struct elfs *e, struct symbol *sym1)
 
 	/* Count orig candidates */
 	for_each_sym_by_demangled_name(e->orig, sym1->demangled_name, sym2) {
-		if (sym2->twin || sym1->type != sym2->type || dont_correlate(sym2) ||
+		if (sym2->twin || sym1->type != sym2->type || sym2->dont_correlate ||
 		    (!maybe_same_file(sym1, sym2)))
 			continue;
 
@@ -550,7 +550,7 @@ static struct symbol *find_twin(struct elfs *e, struct symbol *sym1)
 
 	/* Count patched candidates */
 	for_each_sym_by_demangled_name(e->patched, sym1->demangled_name, sym2) {
-		if (sym2->twin || sym1->type != sym2->type || dont_correlate(sym2) ||
+		if (sym2->twin || sym1->type != sym2->type || sym2->dont_correlate ||
 		    !maybe_same_file(sym1, sym2))
 			continue;
 
@@ -693,7 +693,7 @@ static struct symbol *find_twin_suffixed(struct elf *elf, struct symbol *sym1)
 		return NULL;
 
 	for_each_sym_by_name(elf, name, sym2) {
-		if (sym2->twin || sym1->type != sym2->type || dont_correlate(sym2))
+		if (sym2->twin || sym1->type != sym2->type || sym2->dont_correlate)
 			continue;
 		count++;
 		match = sym2;
@@ -733,7 +733,7 @@ static struct symbol *find_twin_positional(struct elfs *e, struct symbol *sym1)
 	struct symbol *sym2, *match = NULL;
 
 	for_each_sym_by_demangled_name(e->orig, sym1->demangled_name, sym2) {
-		if (sym2->twin || sym1->type != sym2->type || dont_correlate(sym2) ||
+		if (sym2->twin || sym1->type != sym2->type || sym2->dont_correlate ||
 		    !maybe_same_file(sym1, sym2))
 			continue;
 		if (is_tu_local_sym(sym1) != is_tu_local_sym(sym2) ||
@@ -745,7 +745,7 @@ static struct symbol *find_twin_positional(struct elfs *e, struct symbol *sym1)
 	}
 
 	for_each_sym_by_demangled_name(e->patched, sym1->demangled_name, sym2) {
-		if (sym2->twin || sym1->type != sym2->type || dont_correlate(sym2) ||
+		if (sym2->twin || sym1->type != sym2->type || sym2->dont_correlate ||
 		    !maybe_same_file(sym1, sym2))
 			continue;
 		if (is_tu_local_sym(sym1) != is_tu_local_sym(sym2) ||
@@ -777,6 +777,11 @@ static int correlate_symbols(struct elfs *e)
 	struct symbol *sym1, *sym2;
 	bool progress;
 
+	for_each_sym(e->orig, sym1)
+		sym1->dont_correlate = dont_correlate(sym1);
+	for_each_sym(e->patched, sym2)
+		sym2->dont_correlate = dont_correlate(sym2);
+
 	/* Correlate FILE symbols */
 	file1_sym = first_file_symbol(e->orig);
 	file2_sym = first_file_symbol(e->patched);
@@ -817,7 +822,7 @@ static int correlate_symbols(struct elfs *e)
 	do {
 		progress = false;
 		for_each_sym(e->orig, sym1) {
-			if (sym1->twin || dont_correlate(sym1))
+			if (sym1->twin || sym1->dont_correlate)
 				continue;
 			sym2 = find_twin(e, sym1);
 			if (!sym2)
@@ -831,7 +836,7 @@ static int correlate_symbols(struct elfs *e)
 			return -1;
 
 		for_each_sym(e->orig, sym1) {
-			if (sym1->twin || dont_correlate(sym1))
+			if (sym1->twin || sym1->dont_correlate)
 				continue;
 			sym2 = find_twin_suffixed(e->patched, sym1);
 			if (!sym2)
@@ -843,7 +848,7 @@ static int correlate_symbols(struct elfs *e)
 	} while (progress);
 
 	for_each_sym(e->orig, sym1) {
-		if (sym1->twin || dont_correlate(sym1))
+		if (sym1->twin || sym1->dont_correlate)
 			continue;
 		sym2 = find_twin_positional(e, sym1);
 		if (!sym2)
@@ -853,7 +858,7 @@ static int correlate_symbols(struct elfs *e)
 	}
 
 	for_each_sym(e->orig, sym1) {
-		if (sym1->twin || dont_correlate(sym1))
+		if (sym1->twin || sym1->dont_correlate)
 			continue;
 		WARN("no correlation: %s", sym1->name);
 	}
@@ -1066,7 +1071,7 @@ static int mark_changed_functions(struct elfs *e)
 
 	/* Find changed functions */
 	for_each_sym(e->orig, orig_sym) {
-		if (dont_correlate(orig_sym))
+		if (orig_sym->dont_correlate)
 			continue;
 
 		patched_sym = orig_sym->twin;
@@ -1087,7 +1092,7 @@ static int mark_changed_functions(struct elfs *e)
 
 	/* Find added functions and print them */
 	for_each_sym(e->patched, patched_sym) {
-		if (!is_func_sym(patched_sym) || dont_correlate(patched_sym))
+		if (!is_func_sym(patched_sym) || patched_sym->dont_correlate)
 			continue;
 
 		if (!patched_sym->twin) {
@@ -1193,7 +1198,7 @@ static bool klp_reloc_needed(struct reloc *patched_reloc)
 	struct export *export;
 
 	/* no external symbol to reference */
-	if (dont_correlate(patched_sym))
+	if (patched_sym->dont_correlate)
 		return false;
 
 	/* For included functions, a regular reloc will do. */
-- 
2.53.0

Re: [PATCH v2 00/53] objtool/klp: Some klp-build fixes and improvements

[Josh Poimboeuf]

On Thu, Apr 30, 2026 at 09:07:48PM -0700, Josh Poimboeuf wrote:
> Changes since v1 (https://lore.kernel.org/cover.1776916871.git.jpoimboe@kernel.org):
> 
> - Add comment for find_reloc_by_dest_range() first-match behavior
>   [Peter]
> - Simplify is_cold_func() [Peter]
> - Grow __cfi_ symbols [Peter]
> - Rename "Ignore __UNIQUE_ID_*() PCI stub functions" to more general
>   "Don't report uncorrelated functions as new" [Song]
> - Move rodata non-correlation into pointer-comparison fix [Miroslav]
> - Add comments for convert_reloc_sym() return values [Song]
> - Remove redundant SRC/OBJ variables [Song]
> - Use "if (mismatch) {} else" in for_each_sym_by_*() [Song]
> - Flatten nested if-else chain in short-circuit validation [Song]
> - Add comments with examples to symbol correlation algorithm [Song]
> - Move callback refactor to earlier in the patch set [Miroslav]
> - Fix reloc corruption in convert_reloc_sym_to_secsym() [Sashiko]
> - Include offset in object checksum hashing [Sashiko]
> - Fix klp-build checksum comparison output for added/removed
>   instructions [Sashiko]
> - Fix kCFI prefix finding/cloning
> - Add reloc symbol conversion simplification cleanup
> - Improve local label check for uncorrelated symbols
> - Drop "Make function prefix handling more generic" for now (refactored
>   version will come with arm64 patches)
> - Refactor inline alternative cloning into separate
>   clone_inline_alternatives()
> - Add Acked-by/Reviewed-by tags

I'm squashing a few Sashiko nits (see below) into their relevant
patches, along with a minor bisectability issue.

latest is at:

  git://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git klp-build-arm64

diff --git a/scripts/livepatch/klp-build b/scripts/livepatch/klp-build
index 31604d48ff49..10145b1dd089 100755
--- a/scripts/livepatch/klp-build
+++ b/scripts/livepatch/klp-build
@@ -275,7 +275,7 @@ validate_config() {
 		[[ "$CONFIG_AS_VERSION" -lt 200000 ]] &&	\
 		die "Clang assembler version < 20 not supported"
 
-	"$OBJTOOL" klp 2>&1 | command grep -q "not implemented" && \
+	[[ -x "$OBJTOOL" ]] && "$OBJTOOL" klp 2>&1 | command grep -q "not implemented" && \
 		die "objtool not built with KLP support; install xxhash-devel/libxxhash-dev (version >= 0.8) and recompile"
 
 	return 0
@@ -741,7 +741,7 @@ diff_objects() {
 
 		(
 			cd "$ORIG_CSUM_DIR"
-			[[ -v VERBOSE ]] && echo "${cmd[@]}"
+			[[ -v VERBOSE ]] && echo "cd $ORIG_CSUM_DIR && ${cmd[*]}"
 			"${cmd[@]}"							\
 				1> >(tee -a "$log")					\
 				2> >(tee -a "$log" | "${filter[@]}" >&2) ||		\
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index ca360239ea2b..2b03a2d6fc95 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -2494,7 +2494,7 @@ static int __annotate_late(struct objtool_file *file, int type, struct instructi
 			ERROR_INSN(insn, "dodgy NOCFI annotation");
 			return -1;
 		}
-		insn_sym(insn)->nocfi = 1;
+		sym->nocfi = 1;
 		break;
 
 	default: